Add coverage testing using gcov

To check the coverage of e2fsprogs's regression test, do the
following:

	configure --enable-gcov
	make -j8 ; make -j8 check ; make coverage.txt

The coverage information will be the coverage.txt and *.gcov files in
the build directories.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
e2fsck: don't add a UUID on a mounted filesystem with csums

This fix is similar to 66457fcb for tune2fs. When booting from a root
filesystem with an empty UUID which fsck fixes the following remount
step reliably fails, leaving the filesystem in an inconsistent state.
Like the tune2fs fix this patch resolves the issue by simply refusing to
update the UUID if the filesystem is mounted.

Signed-off-by: Michael Marineau <michael.marineau@coreos.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
resize2fs: during shrink, don't free in-use bg data clusters

When freeing a block group descriptor block, be careful not to free
metadata clusters belonging to other groups!

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
resize2fs: don't free in-use clusters when moving blocks

When we're moving blocks around the filesystem, ensure that freeing
the old blocks only frees the clusters if they're not in use by other
metadata.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>