threading: HasLock const function
wrapped pool: IsAlloc constness

This commit changes WrappingPool::IsAlloc to take a const pointer as argument
as pointer isnt modified. ItemPool::IsAlloc is changed to a const function
taking a const poiner as argument.
Merge pull request #50 from zerhacken/minor-fixes

Const correctness fixes in threading.h and wrapped_pool.h
Don't call thread exception handlers on mono that aren't implemented yet