This fixes a few minor things in TLSF.

• As jtenner pointed out, __realloc ignored GC state and required stdlib to deal with RCing, which feels wrong since it requires special care if a block's ref changes, so it now deals with that right away by keeping GC state of the original block. Only relevant for Array's ensureSize with everything else reallocating fresh blocks.
• GC state was partly updated by the direct API methods like __realloc and partly by internals like reallocateBlock, which now is all internal.
• We had asserts meant to execute on API usage only that were at strange places. Even though it did work, this is now separated and checked in a uniform way.