test: don't use wiki urls for documentation comments

Also make consistent use of \ as documentation escape character.

test/testlock.c

@@ -25,7 +25,7 @@ static SDL_threadID mainthread;
 static SDL_Thread *threads[6];
 static SDL_atomic_t doterminate;
 
-/*
+/**
  * SDL_Quit() shouldn't be used with atexit() directly because
  *  calling conventions may differ...
  */