tune2fs: Support for large inode migration.

tune2fs: Support for large inode migration.

Add new option -I <inode_size> to tune2fs.  This is used to change the
inode size. The size need to be multiple of 2 and we don't allow to
decrease the inode size.

As a part of increasing the inode size we increase the inode table
size. We also move the used data blocks around and update the
respective inodes to point to the new block

tune2fs uses the undo I/O manager when migrating to large inode. This
helps in reverting the changes if end results are not correct.  The
environment variable TUNE2FS_UNDO_DIR is used to indicate the
directory within which the tdb file need to be created. The file will
be named tune2fs-<device-name> If TUNE2FS_UNDO_DIR is not set
/var/lib/e2fsprogs is used

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>