Added --disable-dga configure option to disable DGA entirely

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%4017

configure.in

@@ -474,9 +474,13 @@ CheckX11()
                     fi
                 fi
             fi
+            AC_ARG_ENABLE(dga,
+[  --enable-dga            allow use of X11 DGA code [default=yes]],
+                          , enable_dga=yes)
             AC_ARG_ENABLE(video-x11-dgamouse,
 [  --enable-video-x11-dgamouse  use X11 DGA for mouse events [default=yes]],
                           , enable_video_x11_dgamouse=yes)
+            if test x$enable_dga = xyes; then
                 AC_MSG_CHECKING(for XFree86 DGA 1.0 support)
                 video_x11_dga=no
                 AC_TRY_COMPILE([
@@ -494,6 +498,7 @@ CheckX11()
                     fi
                     SYSTEM_LIBS="$SYSTEM_LIBS -lXxf86dga"
                 fi
+            fi
             AC_ARG_ENABLE(video-x11-xv,
 [  --enable-video-x11-xv   use X11 XvImage extension for video [default=yes]],
                           , enable_video_x11_xv=yes)

docs.html

@@ -16,6 +16,7 @@ be found at the <A HREF="http://www.libsdl.org/"> main SDL page</A>.
 Major changes since SDL 1.0.0:
 </H2>
 <UL>
+	<LI> 1.2.1: Added --disable-dga configure option to disable DGA entirely
 	<LI> 1.2.1: Fixed stuck keys when changing the video mode
 	<LI> 1.2.1: Fixed double-mouse event bug on Windows using OpenGL
 	<LI> 1.2.1: Fixed 320x200 video mode on framebuffer console