Add support for unix datagram sockets to UdpInput. Resolves #790.
chmod socket 0666 so everyone can write to it.
Use more staid error message.
Merge branch 'dev' into unixgram-support

Conflicts:
	CHANGES.txt
Merge pull request #852 from mozilla-services/unixgram-support

Add support for unix datagram sockets to UdpInput. Resolves #790.