ocfs2: Allow for debugging of transaction extends

The nastiest cases of transaction extends are also the rarest. We can expose
them more quickly at the expense of performance by going straight to the
journal_restart() in ocfs2_extend_trans(). Wrap things in OCFS2_DEBUG_FS so
that we only do this when "expensive debugging" is turned on.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>