Need diagonal line clipping

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%403373

TODO

@@ -6,6 +6,7 @@
  * Implement desktop video mode change notification?
  * Implement icon support (with translucency?)
  * Add draw blend mode and line drawing support for win32
+ * Add diagonal line clipping to SDL_IntersectRectAndLine()
  * Have Bob look at why DirectColor visuals fail with XA_RGB_BEST_MAP error
  * Verify mouse grab support
  * Properly handle mouse grab with Vista DPI scaling