workaround faulty fltk installs (e.g. in current Debian or Ubuntu)

Fltk/Draw.cpp

@@ -4,7 +4,15 @@
 // bugs and problems to <gmsh@geuz.org>.
 
 #include <FL/gl.h>
-#include <FL/glu.h>
+
+//FIXME: workaround faulty fltk installs
+//#include <FL/glu.h>
+#ifdef __APPLE__
+#  include <OpenGL/glu.h>
+#else
+#  include <GL/glu.h>
+#endif
+
 #include "GUI.h"
 #include "graphicWindow.h"
 #include "GmshDefines.h"

Graphics/drawContext.cpp

@@ -4,7 +4,15 @@
 // bugs and problems to <gmsh@geuz.org>.
 
 #include <FL/gl.h>
-#include <FL/glu.h>
+
+//FIXME: workaround faulty fltk installs
+//#include <FL/glu.h>
+#ifdef __APPLE__
+#  include <OpenGL/glu.h>
+#else
+#  include <GL/glu.h>
+#endif
+
 #include "GmshMessage.h"
 #include "Draw.h"
 #include "drawContext.h"

Graphics/drawGlyph.cpp

@@ -5,7 +5,15 @@
 
 #include <string.h>
 #include <FL/gl.h>
-#include <FL/glu.h>
+
+//FIXME: workaround faulty fltk installs
+//#include <FL/glu.h>
+#ifdef __APPLE__
+#  include <OpenGL/glu.h>
+#else
+#  include <GL/glu.h>
+#endif
+
 #include "drawContext.h"
 #include "Numeric.h"
 #include "Draw.h"

Plugin/CutSphere.cpp

@@ -9,7 +9,15 @@
 
 #if defined(HAVE_FLTK)
 #include <FL/gl.h>
-#include <FL/glu.h>
+
+//FIXME: workaround faulty fltk installs
+//#include <FL/glu.h>
+#ifdef __APPLE__
+#  include <OpenGL/glu.h>
+#else
+#  include <GL/glu.h>
+#endif
+
 #include "Draw.h"
 #endif