Reply message is not always present in reply handler (issue #75)

For example when required.acks is set to 0 there is no reply
and thus no reply message in the reply handler.
Only print test random seed on test failure
Added test for request.required.acks (-1,0,1,2) (issue #75)
Renamed request.required.acks test
Fixed recently induced crash in metadata handling
Added fetch.message.max.bytes and receive.message.max.bytes properties

Previously message.max.bytes was used to limit produce message size,
receive message size and number of bytes to fetch from each topic+partition.
These are unfortunately incompatible and thus requires to be configured
independently.
Proper description for 0008-reqacks test
Correct hint on receive.message.max.bytes
Added "rxcorriderrs" to stats output (unknown correlation ids)
message.send.max.retries did not have effect, no messages were retried (for issue #74)
Only allow one simultaneous topic leader query

This avoids the flood of metadata requests when messagesets start failing
Updated C++ branch info
Version 0.8.3