Merge pull request #1 from rohieb/patch/eglibc-clone

fix FTBFS with (e)glibc: sched.h needs _GNU_SOURCE to be defined for clone() etc.
Newline added.
bind to IPv6 socket by default

On Linux, this is also backwards-compatible and allows users to connect overIPv4
at the same time. Anyway, there shouldn't be many OSes that don't support IPv6
yet, and if there are, they are probably uninteresting.