e2fsck: fix rule-violating lblk->pblk mappings on bigalloc filesystems

e2fsck: fix rule-violating lblk->pblk mappings on bigalloc filesystems

As far as I can tell, logical block mappings on a bigalloc filesystem are
supposed to follow a few constraints:

 * The logical cluster offset must match the physical cluster offset.
 * A logical cluster may not map to multiple physical clusters.

Since the multiply-claimed block recovery code can be used to fix these
problems, teach e2fsck to find these transgressions and fix them.

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