fsck.cramfs: remove define INCLUDE_FS_TESTS

There is only one non-trivial issue where we now print a
warning instead of exit error.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: remove test_fsck.cramfs (reverts 6c32ae78)

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
fsck.cramfs: update man page (--extract and --blocksize)

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
mkfs.cramfs: fix crash when -b 0

Now -b 0 gives us the default (page size) like we do it in
fsck.cramfs.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>