When we replace a multiorder entry, check that all indices reflect the
new value.

Also, compile the test suite with -O2, which shows other problems with
the code due to some dodgy pointer operations in the radix tree code.
Signed-off-by: NMatthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>