[PATCH] schedule_timeout(): improve warning message

Kyle is hitting this warning, and we don't have a clue what it's caused by.
Add the obligatory dump_stack().

Cc: kyle <kylewong@southa.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>