title-folder: fix SDL path on OS X

The Stonesense install script appears to do strange things which cause DF to
load SDL.framework/Versions/A/SDL instead of SDL.framework/SDL. Once the former
is loaded, loading the latter and calling SDL_WM_* functions from it will fail.

A better solution would be to remove parts of the Stonesense fix-libs-*.sh
script(s) that are causing this, since they don't appear to be needed, or
use dlsym() to find the already-opened library/symbols.

plugins/title-folder.cpp

@@ -16,6 +16,7 @@ static std::string original_title;
 static DFLibrary *sdl_handle = NULL;
 static const std::vector<std::string> sdl_libs {
     "SDLreal.dll",
+    "SDL.framework/Versions/A/SDL",
     "SDL.framework/SDL",
     "libSDL-1.2.so.0"
 };