If the query was via multicast, the response isn't matched by
--state ESTABLISHED,RELATED

This fixes #619

The timeout was calculated incorrectly (in each iteration the span between
the start time and the current time was substracted from the timeout
again), and would often become negative, causing warnings in the kernel
log.

sse-multiplex likes to get the header as fast as possible.

error() is a glibc specific function and should not be used in
code meant to be portable.

This is a simple client for gluon-announced.