SCons updates

* libraries are now generated in [BUILD_DIR]/lib
* passed the user_options to all libraries now.
  This means I could remove a couple of Export/Import lines.
* Changed the order in source/blender/src/SConscript and
  source/gameengine/SConscript.
  All libraries are now sorted alphabetically. This has no impact on the build
  process.

source/SConscript

@@ -1,6 +1,6 @@
-Import ('use_gameengine')
+Import ('user_options_dict')
 
 SConscript(['blender/SConscript',
             'kernel/SConscript'])
-if use_gameengine == 'true':
+if user_options_dict['BUILD_GAMEENGINE'] == 1:
     SConscript (['gameengine/SConscript'])