This patch from Chris Davis saves some callback depth, and adds proper
ref-counting to bufferevents when there's a deferred evbuffer callback
inflight. It could use a couple more comments to really nail down what
its invariants are.
svn:r1543
This is code by Chris Davis, with changes to get the unit tests failing less aggressively.
The unit tests for this code do not completely pass yet; Chris is looking into that. If they aren't passing by the next release, I'll turn off this code.
svn:r1499
Either I need to make the callbacks get deferred in a base with no events (doable), or I need to make it okay to call launch_read from inside the callback for read (tricky).
svn:r1277
