Audaspace: porting minor improvements from upstream

- NullDevice is now called None
- Automatic choice of best available device.
- Minor formatting, documentation and cmake fixes.

CMakeLists.txt

@@ -305,6 +305,8 @@ if(NOT WIN32)
   if(UNIX AND NOT APPLE)
     option(WITH_JACK_DYNLOAD  "Enable runtime dynamic JACK libraries loading" OFF)
   endif()
+else()
+  set(WITH_JACK OFF)
 endif()
 if(UNIX AND NOT APPLE)
   option(WITH_SDL_DYNLOAD  "Enable runtime dynamic SDL libraries loading" OFF)
@@ -671,16 +673,8 @@ if(NOT WITH_BLENDER AND NOT WITH_CYCLES_STANDALONE)
   )
 endif()
 
-if(NOT WITH_AUDASPACE)
-  if(WITH_OPENAL)
-    message(WARNING "WITH_OPENAL requires WITH_AUDASPACE which is disabled")
-    set(WITH_OPENAL OFF)
-  endif()
-  if(WITH_JACK)
-    message(WARNING "WITH_JACK requires WITH_AUDASPACE which is disabled")
-    set(WITH_JACK OFF)
-  endif()
-endif()
+set_and_warn_dependency(WITH_AUDASPACE WITH_OPENAL OFF)
+set_and_warn_dependency(WITH_AUDASPACE WITH_JACK OFF)
 
 if(NOT WITH_SDL AND WITH_GHOST_SDL)
   message(FATAL_ERROR "WITH_GHOST_SDL requires WITH_SDL")