AlienImage (TKService) should not depend on X11

[dbarbier]

AlienImage_X11XWDAlienData.cxx and AlienImage_X11XWDFileHeader.cxx include X11/Xlib.h because they need X macros.

Maybe we can remove this dependency by defining the few macros needed. A first step is to include X11/X.h instead of X11/Xlib.h.

[dbarbier]

Here are some additional information, this issue is quite complex and my description was pretty dumb.

In OCCT, OCAF and Data Exchange components depend on Visualization. Some people want to install OCCT on machines without an X server, so a proposal has been made on Debian list to split components:
http://lists.debian.org/debian-science/2008/01/msg00023.html
This proposal has been implemented almost as described.

In OCE, the situation is quite different, I did not want to introduce new components (OCAF-lite and DE-lite). And when cross-compiling for Mingw, TKService caused trouble because my cross-compiler does not have X11 stuff. So in order to compile the maximum stuff, an option has been added to compile TKService with or without X11 support (see commit 68d1d35).

Then OSX users also told that they want to get rid of X11 stuff whenever possible.

This explains the current mess, it would surely be a good idea to think about this issue from scratch and find a better plan.