Fixed findSlabClassIndex() for non-contiguous access.
Fixed findSlabClassIndex() for non-contiguous access.

THe previous code only worked when the user asked for the next
immediate slab class, but would fail they asked for a slab class a few
slots ahead.  Using recursion as a quick and inefficient fix.

magiccao/go-slab,idada/go-slab,couchbase/go-slab,steveyen/go-slab