[PATCH] radix-tree: reduce tree height upon partial truncation

Shrink the height of a radix tree when it is partially truncated - we only do
shrinkage of full truncation at present.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>