libblkid: detect squashfs 3 vs 4

Detect squashfs version <= 3 as squashfs3 and version >= 4 as squashfs.

squashfs kernel module version 4.0 (kernel 2.6.29) is not backward
compatible to open squashfs created with previous versions.

Also fixed version number parsing, see
$  mkdir test
$  mksquashfs test test.sqsh
$  blkid -p test.sqsh
- test.sqsh: VERSION="1024.0" TYPE="squashfs" USAGE="filesystem"
+ test.sqsh: VERSION="4.0" TYPE="squashfs" USAGE="filesystem"

This patch comes from openSUSE / SLE. Original author was probably
Miklos Szeredi.
Internal SUSE references: bnc#666893, sr226509

CC: Stanislav Brabec <sbrabec@suse.cz>
CC: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>