e2fsck: consistently use ext2fs_get_mem()

e2fsck: consistently use ext2fs_get_mem()

Consistently use ext2fs_get_mem() and ext2fs_free_mem() instead of
calling malloc() and free() directly in e2fsck.  In several places
it is possible to use ext2fs_get_memzero() instead of explicitly
calling memset() on the memory afterward.

This is just a code cleanup, and does not fix any specific bugs.

[ Fix up library dependencies in e2fsck/Makefile.in to fix "make
  check" breakages. -- TYT ]

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Lustre-bug-id: https://jira.whamcloud.com/browse/LU-13197
Signed-off-by: Theodore Ts'o <tytso@mit.edu>