mapAlreadyAskedFor gets additions when AlreadyHave() #1347

Without this change, mappings will be created even after AlreadyHave equals true, and will never be erased.

A small fix, probably would never have caused a problem, other than filling unbounded and potentially using up more memory than needed. Might be quite significant is bitcoind is left running for a long period of time.

@jgarzik I would argue that had this mapping been named mapWaitingFor (as per #1341), this bug would have been less likely to have occurred, since upon renaming it becomes more intuitively obvious that it's in the wrong place in the code.

I do think quite strongly that #1341 should be re-opened for some discusssion. If POLA isn't a good reason for a variable name change, then what is?

How should this change be tested?

Not tested, but @rebroad's reasoning sounds correct to me. mapAlreadyAskedFor contains getdata requests that have not been answered yet. If AlreadyHave() returns true for an inv, there is no reason to keep waiting for it.

mmm. I feel like I'll regret this, but ACK.