[PATCH] slab cleanup

slab.c has become a bit revolting again.  Try to repair it.

- Coding style fixes

- Don't do assignments-in-if-statements.

- Don't typecast assignments to/from void*
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>