Reduce dependency on scrollkeeper (#743318)

Scrollkeeper and the associated OMF catalog files are used by the
GNOME 2 version of yelp to display the GParted help manual.  To see how
this works try the following command:

  yelp ghelp:gparted

GNOME version 3 and higher yelp do not require scrollkeeper or the OMF
catalog files to properly display the GParted help manual.  And in fact
GNOME 3 deprecated the GNOME 2 method of building and installing GNOME
help documents altogether; including use of GNOME_DOC_INIT autoconf
macro, the gnome-doc-utils package and use of scrollkeeper.

  [GNOME 3] GNOME Goal: Port To New Documentation Infrastructure
  https://wiki.gnome.org/Initiatives/GnomeGoals/NewDocumentationInfrastructure

Further, the next release of Debian, Debian 10 (Buster), will be
removing the scrollkeeper / rarian package.

  rarian: Don't release with Buster
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=885657

GParted is still a GNOME 2 app using GNOME 2 documentation build system
using autoconf GNOME_DOC_INIT macro.

  [GNOME 2] Migrating your documentation to gnome-doc-utils
  https://wiki.gnome.org/Projects/GnomeDocUtils/MigrationHowTo

This is needed to build GParted documentation on still supported GNOME 2
distributions RHEL / CentOS 6.  So avoid requiring deprecated
scrollkeeper on GNOME 3 by automatically disabling scrollkeeper database
updates when the scrollkeeper-update command is not available.

  Executable          | Configure option used  | Use scrollkeeper
  scrollkeeper-update | on command line        | when building help
  exists?             |                        | for GParted?
  --------------------+------------------------+-------------------
  Yes                 | <none>                 | Yes
  Yes                 | --enable-scrollkeeper  | Yes
  Yes                 | --disable-scrollkeeper | No
                      |                        |
  No                  | <any>                  | No

Note that because GParted is still using the GNOME 2 documentation build
system it still builds and installs OMF files.  It is just that they are
not required with GNOME 3 yelp and this commit automatically disables
updating the scrollkeeper database when the scrollkeeper-update command
is not available.

Bug 743318 - configure script missing check for scrollkeeper dependency

README

@@ -102,8 +102,8 @@ b. Building from Source
    On Fedora, you will need to run (as root);
       yum install gtkmm24-devel parted-devel e2fsprogs-devel gettext \
                   'perl(XML::Parser)' desktop-file-utils libuuid-devel \
-                  gnome-doc-utils docbook-dtds rarian-compat intltool \
+                  gnome-doc-utils docbook-dtds intltool gnome-common \
-                  gnome-common gcc-c++
+                  gcc-c++
       yum groupinstall 'Development Tools'
 
    On openSUSE, these dependencies may be obtained by running the
@@ -123,9 +123,13 @@ b. Building from Source
    the --disable-doc flag:
       E.g., ./configure --disable-doc
 
-   If you wish to build this package for use on a desktop that does not
+   Scrollkeeper is needed on GNOME/Gtk 2 desktops to update the OMF
-   support scrollkeeper use the --disable-scrollkeeper flag:
+   catalog files to allow yelp to display the GParted help manual.  On
+   GNOME/Gtk 3 desktops scrollkeeper in not required.  Use can be
+   explicitly disabled with the --disable-scrollkeeper flag:
       E.g., ./configure --disable-scrollkeeper
+   Note that the configure script will automatically disable
+   scrollkeeper if the scrollkeeper-update command is not found.
 
    If you wish to build this package to use native libparted /dev/mapper
    dmraid support use the --enable-libparted-dmraid flag:

configure.ac

@@ -348,6 +348,23 @@ fi
 
 AM_CONDITIONAL([BUILD_HELP_DOC], [test "x$enable_doc" = xyes])
 
+dnl GNOME 2 yelp needs scrollkeeper database updates to find installed GNOME help files.
+dnl GNOME 3 yelp doesn't need scrollkeeper and its use is deprecated.  To avoid requiring
+dnl deprecated scrollkeeper on GNOME 3, automatically disable scrollkeeper database
+dnl updates when the command is not available.
+dnl (See /usr/share/aclocal/gnome-doc-utils.m4 for the GNOME_DOC_INIT macro which has
+dnl already parsed the --disable-scrollkeeper option and set enable_scrollkeeper and
+dnl ENABLE_SK).
+AC_CHECK_PROG([have_scrollkeeper_update], [scrollkeeper-update], yes, no)
+AC_MSG_CHECKING([whether to enable scrollkeeper database update])
+if test "$enable_scrollkeeper" = "yes" -a "$have_scrollkeeper_update" = "yes"; then
+	AC_MSG_RESULT([yes])
+else
+	enable_scrollkeeper=no
+	AM_CONDITIONAL([ENABLE_SK], false)
+	AC_MSG_RESULT([no])
+fi
+
 
 dnl======================
 dnl check whether to use native libparted dmraid support
@@ -438,6 +455,7 @@ echo "======================== Final configuration ==========================="
 echo "                         Installing into prefix  :  $prefix"
 echo ""
 echo "                      Build help documentation?  :  $enable_doc"
+echo "                  Update scrollkeeper database?  :  $enable_scrollkeeper"
 echo ""
 echo "           Use native libparted dmraid support?  :  $enable_libparted_dmraid"
 echo ""