Merge pull request #308 from minrk/exceptions

add Again and ContextTerminated exception subclasses
Merge pull request #311 from minrk/greenbarf

tweak gevent bug workarounds

- [x] timeout is configurable, and now long (11.6 seconds, to avoid timeout coincidences)
- [x] debug message is off by default

ref: #229
remove last use of allocate

just use malloc instead