Document blkid command as a mandatory requirement (#753436)

Update the README file to document the blkid command as a mandatory
requirement for GParted.  GParted will run without blkid but it is
needed to detect a number of file systems which libparted doesn't and in
a number of other situations.

Blkid is needed to detect these file systems:
    exfat
    f2fs
    ReFS
    SWRaid
    ZFS

Blkid also detects these file systems (for which GParted has simple
internal detection but libparted, mostly, doesn't detect):
    btrfs      (detected by libparted >= 3.2)
    LVM2 PV
    LUKS
    nilfs2     (detected by libparted >= 2.4)
    reiser4

Blkid is also needed for these commits:

1)  f8faee6377
    Avoid whole disk FAT being detected as MSDOS partition table (#743181)
    (with libparted 1.9.0 to 2.3 inclusive)

2)  9e5e9f5627
    Enhance file system detection to use FS_Info method - blkid
    (Detect file systems with sector sizes other than 512 bytes with
    libparted 2.2)

Other changes to the DISTRIBUTION NOTES section of the README file:
* Drop NOTE about vol_id and blkid being used to read volume labels for
  specific file systems and read the UUIDs.  Vol_id was deprecated in
  May 2009 and is not included in any currently supported distribution.
  Blkid is now mandatory.  List of optional commands at the end of the
  section seems to cover everything that is necessary.
* Indent description of optional commands at the end of the section to
  match the indentation earlier in the section.
* Line wrap the section at column 72 to match the rest of the file.

Bug 753436 - Update documentation of GParted software dependencies

README

@@ -190,15 +190,22 @@ src      - contains C++ source code
 
 DISTRIBUTION NOTES
 ------------------
-Gparted uses GNU libparted to detect and manipulate devices and partition
+GParted uses GNU libparted to detect and manipulate devices and
-tables.  Several optional packages provide additional file system support.
+partition tables.  The blkid command is also required to detect those
-Optional packages include:
+file systems which libparted doesn't detect.  (The blkid command should
+be considered a mandatory requirement).
+
+GParted also queries and manipulates the file systems within those
+devices and partitions.  When available, it uses each file system's
+specific commands.  The following optional file system specific packages
+provide this support:
 
    btrfs-tools
    e2fsprogs
    f2fs-tools
    dosfstools
-   mtools          - required to read and write FAT16/32 volume labels and UUIDs
+   mtools          - required to read and write FAT16/32 volume labels
+                     and UUIDs
    hfsutils
    hfsprogs
    jfsutils
@@ -208,24 +215,16 @@ Optional packages include:
    reiserfsprogs
    xfsprogs, xfsdump
 
-   NOTE:  * If the vol_id command is in the search PATH, it will be used
-            to read linux-swap, reiser4, hfs, and hfs+ file system
-            volume labels.
-          * If the blkid command is in the search path, it will be used
-            to read file system UUIDs and labels.  It is also used for
-            ext4 file system detection.
-            blkid is part of the util-linux package and e2fsprogs
-            package before that.
-
 
 For dmraid support, the following packages are required:
 
    dmsetup         - removes /dev/mapper entries
-   dmraid          - lists dmraid devices and creates /dev/mapper entries
+   dmraid          - lists dmraid devices and creates /dev/mapper
+                     entries
 
 For GNU/Linux distribution dmraid support, the following are required:
-   - kernel built with Device Mapping and Mirroring built.  From menuconfig,
+   - kernel built with Device Mapping and Mirroring built.  From
-     it is under Device Drivers -> <something> (RAID & LVM).
+     menuconfig, it is under Device Drivers -> <something> (RAID & LVM).
    - dmraid drive arrays activated on boot (e.g., dmraid -ay).
 
 
@@ -239,10 +238,11 @@ is required:
    gpart           - guesses PC-type hard disk partitions
 
 
-Several more commands are optionally used by GParted if found on the system.
+Several more commands are optionally used by GParted if found on the
-These commands include:
+system.  These commands include:
 
-   blkid         - used to read volume labels and detect ext4 file systems
+   blkid           - [mandatory requirement] used to detect file systems
+                     libparted doesn't, read UUIDs and volume labels
    hdparm          - used to query disk device serial numbers
    vol_id          - used to read volume labels
    udisks          - used to prevent automounting of file systems
@@ -251,16 +251,19 @@ These commands include:
                      file systems.  (e.g., nautilus, pcmanfm)
    hal-lock        - used to prevent automounting of file systems
    gksudo          - used to acquire root privileges in .desktop file,
-                   but only if available when gparted source is configured.
+                     but only if available when gparted source is
-   gksu          - alternatively used to acquire root privileges in .desktop
+                     configured.
-                   file if gksu not available, but only if available when
+   gksu            - alternatively used to acquire root privileges in
-                   gparted source is configured.
+                     .desktop file if gksu not available, but only if
-   kdesudo       - alternatively used to acquire root privileges in .desktop
+                     available when gparted source is configured.
-                   file if gksudo and gksu not available, but only if available
+   kdesudo         - alternatively used to acquire root privileges in
-                   when gparted source is configured.
+                     .desktop file if gksudo and gksu not available, but
-   xdg-su        - alternatively used to acquire root privileges in .desktop
+                     only if available when gparted source is
-                   file if gksudo, gksu, and kdesudo are not available, but only
+                     configured.
-                   if available when gparted source is configured.
+   xdg-su          - alternatively used to acquire root privileges in
+                     .desktop file if gksudo, gksu, and kdesudo are not
+                     available, but only if available when gparted
+                     source is configured.
    udevinfo        - used in dmraid to query udev name
    udevadm         - used in dmraid to query udev name
    yelp            - used to display help manual