merged mahendra/zkcommit into 0.8.0beta1
add missing import for KafkaConnectionError
KafkaClient: make it clear where communication error happened, in sending request or in receiving response.
merged 0.8.0beta1, 1 conflict
replace simplejson with standard json, with an option to use ujson if available.
raise explicit Exception if no live brokers can be found, instead of ReferneceError
move gevent dependent code in a separate module so that kafka-python works without gevent installed.