Raise exc if TokenAware + M3P + no murmur3 ext

Instead of logging a warning, if the TokenAwarePolicy is used with a
cluster that uses the Murmur3Partitioner, but the murmur3 extension has
not been compiled, an exception will be raised when Cluster.connect() is
called.
Always use Cluster policies in control connection

Before this fix, if the cluster's load_balancing_policy or
reconnection_policy were set after __init__() but before connect(), the
control connection would not observe the change and would continue to
use the wrong policies.
Pass errno to libev read/write handlers on error

Previously, the error would be set for the current thread, so whatever
the next line of Python that was interpreted in that thread was would
see the error.  Instead, this passes the errno to the appropriate
handler function, allowing the connection to be defuncted.
Don't re-declare result variable