Fix #119, test_gc crashes silently
Fix #119, test_gc crashes silently

When the collection kicks in our variable stored in fast locals
has been freed but is still in fast locals.  We need to first replace
the value in fast locals and then decref the old value after
the new value is stored.

Microsoft/Pyjion,Microsoft/Pyjion,brettcannon/Pyjion,DinoV/Pyjion-1,brettcannon/Pyjion,brettcannon/Pyjion,Microsoft/Pyjion,DinoV/Pyjion-1,DinoV/Pyjion-1,DinoV/Pyjion-1,Microsoft/Pyjion