Added love.filesystem.getRealDirectory(filepath).

It returns the platform-specific full path of the directory containing the filepath (rather than the file.) For example, if 'saves/save1.txt' exists in the save directory, love.filesystem.getRealDirectory("saves/save1.txt") will equal love.filesystem.getSaveDirectory().

src/modules/filesystem/wrap_Filesystem.h

@@ -56,6 +56,7 @@ int w_getUserDirectory(lua_State *L);
 int w_getAppdataDirectory(lua_State *L);
 int w_getSaveDirectory(lua_State *L);
 int w_getSourceBaseDirectory(lua_State *L);
+int w_getRealDirectory(lua_State *L);
 int w_exists(lua_State *L);
 int w_isDirectory(lua_State *L);
 int w_isFile(lua_State *L);