Add EXT_JOURNAL to the blkid tag of ext3 filesystems.

Add EXT_JOURNAL to the blkid tag of ext3 filesystems.

If the filesystem has an external journal, store the UUID of the
external journal in the tag EXT_JOURNAL.

If the filesystem type has changed, clear all the tags on the device,
not just a preset list of LABEL, UUID, TYPE, and SEC_TYPE.

Fix a bug so that blkid_set_tag will work correctly when freeing a tag
when the input name parameter comes from the tag that we are freeing.

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