* implemented some stuff to find a good blocksize to use for
copy/move. Actually i'm not really happy with it, because probing
seems suboptimal, but it's better than nothing. As soon as i have
some time i should do some research on the subject to find a better
solution.
* include/Dialog_Partition_Copy.h,
include/GParted_Core.h,
include/OperationCopy.h,
include/Win_GParted.h,
src/Dialog_Partition_Copy.cc,
src/GParted_Core.cc,
src/OperationCopy.cc,
src/Win_GParted.cc: made blocksize settable by the user.