There's a bunch of definitions in xfs_trans.h that define on-disk
formats - transaction headers that get written into the log, log
item type definitions, etc. Split out everything into a separate
file so that all which remains in xfs_trans.h are kernel only
definitions.

Also, remove the duplicate magic number definitions for
XFS_TRANS_MAGIC...
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NBen Myers <bpm@sgi.com>