Login: define XDG_RUNTIME_DIR to enable sound in user session.

Author: trunkmaster

Applications/Login/UserSession.m

@@ -103,6 +103,7 @@ - (BOOL)_setUserEnvironment
   setenv("LC_CTYPE", "en_US.UTF-8", 1);
   setenv("DISPLAY", ":0", 1);
 
+  setenv("XDG_RUNTIME_DIR", [[NSString stringWithFormat:@"/run/user/%i", user->pw_uid] cString], 1);
   setenv(
       "PATH",
       [[NSString