Add support for backing up the journal inode location in the

Add support for backing up the journal inode location in the
superblock.  E2fsck will automatically save the journal information
in the superblock if it is not there already, and will use it if the
journal inode appears to be corrupted.  ext2fs_add_journal_inode()
will also save the backup information, so that new filesystems
created by mke2fs and filesystems that have journals added via
tune2fs will also have journal location written to the superblock as
well.  Debugfs's logdump command has been enhanced so that it can
use the journal information in the superblock.

The debugfs man page has been improved to more fully describe the
logdump command.

Added two new functions, ext2fs_file_open2() and
ext2fs_inode_io_intern2() which take a pointer to an inode structure;
this is needed so that e2fsck and debugfs can synthesize a
fake journal inode and use it to access the journal.