Don't balance on clone by default.

Balance on clone has a number of trivial performance failure cases, but it was
needed to get decent OpenMP performance on NUMA (Opteron) systems.  Not doing
child-runs-first for new threads also solves this problem in a nicer way
(implemented in a previous patch).
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>