Instance should not be freed to pool twice

[samreid]

Currently it is possible to free an instance to the pool twice, which could lead to disasterous results (since it could be popped from the pool twice and mutated by different clients).

Possible solutions:

1. Add a check to the pool to make sure an instance is not already in the pool (by iterating over the existing pool when an item is added to the pool)
2. Add a field to Poolable instances that indicates whether they are alive or in the pool
3. Add your own idea here!

[pixelzoom]

Presumably this issue is referring to Poolable.