Complete message write to socket when socket cannot accept all bytes.

fwrite to a socket may not write all the requested bytes, so keep sending
remaining bytes until done. Wait for the socket to be ready for writing
between each attempt using the default send timeout value.
Merge branch 'largebuf' into fwritebug

Conflicts:
	src/lib/Kafka/Socket.php

Basically, I'm merging in the code I will submit as a pull request to
upstream into this working branch that I am sharing with my $(coworkers)
for now.