e2fsck: optimize the inserting of dir_info_db

e2fsck: optimize the inserting of dir_info_db

Binary search is now used when inserting an dir info to the array.
Memmove is now used when moving array. Both of them improves
the performance of inserting.

This patch is also a prepartion for the merging of two dir db
arrays.

E2fsprogs-commit: 13d3c76475d050941d244c85cbb9256ffd980f88

Change-Id: I69041084dbd7e36eefa44744c3fb3737af8e906e
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>