Building with -ansi failed due to some code (as well as system
headers) using non-C89 features. Fix that by adding the usual
_POSIX_SOURCE and _BSD_SOURCE definitions already present in some
other files.

Using C++-style comments when building the code with -ansi does not
work, so be more conservative with the comment style.

build_dir/rfb is not passed as an include directory automatically to
the compiler, so including that file fails.

So far, libgcrypt was looked for but no targets linked against it
directly; this caused linking problems for the client and server
examples, as the symbols they needed were not passed to the linker.

The issue that the GnuTLS websockets code uses libgcrypt regardless of
whether it has been found or not has not been touched by this commit,
though.

As requested only those lines are indented that have been changed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Signed-off-by: Rostislav Lisovy <lisovy@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

The various other headers include windows.h and the winsock headers
which give an error when SOCKET and socklen_t are already defined.

Needed for the IPv6 stuff.

These check for optional modules.

TightPNG replaces the ZLIB stuff int Tight encoding with PNG. It still
uses JPEG rects as well. Theoretically, we could build TightPNG with only
libpng and libjpeg - without zlib - but libpng depends on zlib, so this is
kinda moot.

This also fixes a compiler warning.

Conflicts, resolved manually:
	AUTHORS

Original thread: http://sourceforge.net/tracker/?func=detail&aid=3310255&group_id=32584&atid=405860