Return ENOMEM from nn_allocmsg (fixes #175)

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
protocol.h and transport.h files are not installed

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
FreeBSD can return ECONNRESET from close()

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
sendmsg on FreeBSD can return ENOTCONN

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Update nn.h

copy paste issue from socket.h

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Emeric Chevalier added to AUTHORS file.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>