configure now defines XMESA if you have GL/xmesa.h. Also added #undef for

_EXPERIMENTAL_.  Code that really isn't ready for production should go
under this define (which you must currently specifically turn on..)  This
is primarily for things like the GL waterwarp and multitexture which are
in some ways broken and otherwise not a good idea to use at the moemnt in
the release without having to remove the code.

acconfig.h

@@ -10,6 +10,9 @@
 /* Define this to something sane if you don't have stricmp */
 #undef stricmp
 
+/* Define this if you are using Mesa */
+#undef XMESA
+
 /* Define this if you have GL_COLOR_INDEX8_EXT in GL/gl.h */
 #undef HAVE_GL_COLOR_INDEX8_EXT
 
@@ -22,6 +25,9 @@
 /* Define this if you have a BSD-style CD-ROM API */
 #undef USE_BSD_CD
 
+/* Define this to use experimental code */
+#undef _EXPERIMENTAL_
+
 #if defined(X11)
 #   define OUTPUT_STR	"X11"
 #elif defined(GGI)

configure.in

@@ -231,6 +231,7 @@ if test "x$HAS_OGL" != xno; then
    CPPFLAGS="$CPPFLAGS $OGL_CFLAGS"
    AC_CHECK_HEADER(GL/gl.h, HAS_OGL=yes, HAS_OGL=no)
    if test "x$HAS_OGL" != xno; then
+      AC_CHECK_HEADER(GL/xmesa.h, HAS_XMESA=yes, HAS_XMESA=no)
       AC_MSG_CHECKING(for GL_COLOR_INDEX8_EXT in GL/gl.h)
       AC_TRY_COMPILE([#include "GL/gl.h"],
         [ int x = (int) GL_COLOR_INDEX8_EXT;],
@@ -347,6 +348,10 @@ if test "x$HAS_OGL" = xyes; then
 fi
 if test "x$HAS_OGL" != xyes; then
    OGL_CFLAGS="" OGL_LIBS=""
+else
+   if test "xHAS_XMESA" = xyes; then
+      AC_DEFINE(XMESA)
+   fi
 fi
 
 dnl Check for xil