Message 116284 - Python tracker

It seems we need to clarify the return value of PyThread_create_key. The patch returns 0 in case of failure, which is clearly wrong as 0 is also a valid key.

I think it's safe to return -1: TlsAlloc returns TLS_OUT_OF_INDEXES, which is 0xFFFFFFFF, i.e. -1 on a 32-bit system.