Check for a busy device when creating a journal.

Check for a busy device when creating a journal.

In ext2fs_add_journal_inode() check for the case where the filesystem
appears to be unmounted, but the device is still apparently busy.
This can happen when the luser doesn't bother to mount /proc and has a
bogus /etc/mtab, but still wants to mount the filesystem before using
tune2fs(?!?).  Add a safety check to save him from his own stupidity,
at least on 2.6 kernels.  (Addresses Debian Bug #319002)

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>