[PATCH] JFS: Don't allocate extents that overlap existing extents

Modify xtSearch so that it returns the next allocated block when the
requested block is unmapped.  This can be used to make sure we don't
create a new extent that overlaps the next one.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>