Audaspace: fixing problems for the merge to master suggested by Campbell and Sergey.

- rename WITH_EXTERNAL_AUDASPACE to WITH_SYSTEM_AUDASPACE.
- rename C/PYAUDASPACE to AUDASPACE_C/PY
- simplifying cmake defines and includes.
- fixing include paths and enabling WITH_SYSTEM_AUDASPACE for windows.
- fixing scons building.
- other minor build system fixes.

source/gameengine/Ketsji/KX_PythonInit.cpp

@@ -61,7 +61,7 @@ extern "C" {
 
 	#  include "marshal.h" /* python header for loading/saving dicts */
 }
-#include "AUD_PyInit.h"
+#include "../../../../intern/audaspace/intern/AUD_PyInit.h"
 
 #endif  /* WITH_PYTHON */