Don't expose X11 headers in user space any more (mostly).

Platform headers should not be #include'd in public FLTK header files,
so that user space is not polluted by platform specific definitions.

This commit fixes FL/fl_utf8.h to #include X11 headers only if compiled
in the FLTK library.

Todo (FLTK 1.4): Remove more unnecessary (unwanted) system header #include
statements from FL/x.H and other public header files.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@11266 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

CHANGES

@@ -60,6 +60,8 @@ CHANGES IN FLTK 1.3.4					RELEASED: ??? ?? 2016
 	  or not (STR #3142). It also captures subwindows of GL windows.
 	- Fl::delete_widget() now hides the widget or window immediately
 	  (i.e. when called) - only destruction is delayed as before.
+	- FLTK header files don't expose X11 definitions in user code any more
+	  unless required by including FL/x.H explicitly or implicitly.
 	- The PostScript code output when printing images under Linux/Unix
 	  is quite smaller due to use of lossless compression techniques.
 	- The Linux/Unix printer dialog now uses BSD-style printing commands

FL/fl_utf8.h

@@ -60,8 +60,10 @@
 #else /* X11 */
 #  include <sys/types.h>
 #  include <sys/stat.h>
-#  include <X11/Xlocale.h>
-#  include <X11/Xlib.h>
+#  if defined(FL_LIBRARY) /* don't expose X11 headers in user space */
+#    include <X11/Xlocale.h>
+#    include <X11/Xlib.h>
+#  endif /* defined(FL_LIBRARY) -- don't expose X11 headers in user space */
 #  include <locale.h>
 #  define xchar unsigned short
 #endif