e2fsck,libquota: Update quota only if its inconsistent

e2fsck,libquota: Update quota only if its inconsistent

Currently fsck recomputes quotas and overwrites quota files
whenever its run. This causes unnecessary modification of
filesystem even when quotas were never inconsistent. We also
lose the limits information because of this. With this patch,
e2fsck compares the computed quotas to the on-disk quotas
(while updating the in-memory limits) and writes out the
quota inode only if it is inconsistent.

Signed-off-by: Aditya Kali <adityakali@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>