The core of this fix is a threadsafe, fair Queue class. It is
very similar to Queue in stdlib except that it supports waiting
with a timeout.
The issue this solves is that if several threads are contending for
database connections, an unfair queue makes is possible that a thread
will timeout even while other threads successfully acquire and release
connections. A fair queue means the thread that has been waiting the
longest will get the next available connection.
This includes a few test fixes to avoid test ordering issues that
cropped up during development of this patch.