Until now, they were forwarded to processing, but this makes no sense
Also, it looks like the system seems to provide a zero return code
on a UDP recvfrom() from time to time for some internal reasons. These
"receives" are now silently ignored.

A comparison was done between the current and the former source address.
However, this was done on the full sockaddr_storage structure and not
on the host address only. This has now been changed for IPv4 and IPv6.
The end result of this bug could be a higher UDP message loss rate than
necessary (note that UDP message loss can not totally be avoided due
to the UDP spec)

- saved gettimeofday() calls in imtcp (and increased reception buffer)
- somewhat optimized stringbuf.c
- some other optimizations

Conflicts:
	tests/Makefile.am

Conflicts:
	tests/Makefile.am

Well, actually this and a lot of related things. I improved the
testbench so that the new capabilities are automatically tested and
also did some general cleanup. The current multiple tcp listener
solution will probably receive some further cleanup, too, but looks
quite OK so far. I also reviewed the way tcpsrv et all work, in
preparation of using this code for imdiag. I need to document the
findings, especially as the code is rather complicated "thanks" to
the combination of plain tcp and gssapi transport modes.

Thanks to Michael Biebl for helping to debug this one.

Conflicts:
	ChangeLog
	Makefile.am
	configure.ac
	doc/manual.html

pkg-config uses uppercase for its _CFLAGS and _LIBS variable names.
So we follow suit and convert all _cflags and _libs variables to
uppercase for more consistency.