Haigha

=====

Fix handling of socket timeouts in gevent transport

=====

Client sends heartbeat frames on its own rather than simply replying to ones
received from the broker

=====

Channel close listeners are now notified before channel local data is cleaned
up

Default to the gevent transport

Removed fixed requirements for libevent or gevent. It is now up to the user to
install the packages corresponding to their preferred transport.

=====

Added a write lock around GeventTransport.write() call to socket.sendall()

=====

Fixed handling of channel closures due to error. This cleaned up several DoS
vulnerabilities, including a lockup in the ChannelPool, unbounded memory
consumption, and failure to re-use channel ids after max id enumerator
rolled over. Channel cleanup relies on reference counting to ensure a client
can respond to rapid opening and closing of channels.

Fixed failure to always cast GeventTransport.read() return to a bytearray,
which caused problems when reading partial frames.

Fixed failure in GeventTransport to switch to non-blocking socket after
connecting.

Fixed fetching of close_info when connection close callback executes.

=====

Abstracted libevent requirement and added support for gevent backend

Support non-blocking connect on libevent transport

Removed connection strategies from Connection and deleted ConnectionStrategy
class. Combined with a simplified and abstracted approach to IO and scheduling
in the Transports, the strategy for failed connections is more deterministic
and left in the hands of the user.