Add IN6_IS_ADDR_* macros and other IPv6 stuff.
Make AF_UNIX and AF_INET different.

GNUnet contains a switch with cases for AF_UNIX and AF_INET.
Fix prototypes for stat64, fstat64, lstat64.
Add some IPv6 stuff to netinet/in.h.
Move initgroups outside of !_XOPEN_SOURCE.

It was put into newlib grp.h revision 1.2 by Edward M. Lee,
but every other system's grp.h I looked at doesn't do this.
Define SA_RESTART.
Define timezone.
Merge pull request #1328 from amatus/push-upstream

Fixes for GNUnet compile.