blkid: add fallback to ext4 for 2.6.29+ kernels if ext2 is not present

blkid: add fallback to ext4 for 2.6.29+ kernels if ext2 is not present

Starting in 2.6.29, ext4 can be used to support filesystems without a
journal.  So if ext2 is not present, and the kernel version is greater
than 2.6.29, and ext4 is present, return a filesystme type of ext4.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> blkid: Add fallback to
ext4 for 2.6.29+ kernels if ext2 is not present

Starting in 2.6.29, ext4 can be used to support filesystems without a
journal.  So if ext2 is not present, and the kernel version is greater
than 2.6.29, and ext4 is present, return a filesystme type of ext4.

[kzak@redhat.com: port from e2fsprogs to util-linux-ng tree]

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Karel Zak <kzak@redhat.com>