Added TAGS to .gitignore
Merge branch 'master' into conn-signal
Fixed Garbage Collection Queue bug

Fixed bug introduced in new "single queue" change from a couple days ago. The
bug is that a multiplexer thread could dereference a signal in the Garbage
Collection Queue for which it didn't have a reference. This happened if a signal
got added to the GC Queue after a thread exited its wait state but before it
iterated through the GC Queue. The thread would dereference the signal at the
end of the queue even though the signal was not referenced by the thread.

The fix is that multiplexer threads finish garbage collection co-atomically with
exiting their wait state.