getlantern/lantern#1895 Fixed problem with opening too many connections

@myleshorton This was the crux of the problem.  Anytime that I needed to add connections, I would launch a goroutine that would add the number of connections that I thought I needed at the time.  If we entered this code again before that first goroutine finished, the second attempt would think that it needs more connections than it actually does, and so on.