Make all uses of the Steps* in the TrailEntry class use an accessor method.

This makes it simple to switch to something else, such as using a StepsId
instead of a Steps*.

stepmania/src/SongManager.cpp

@@ -1144,7 +1144,7 @@ bool SongManager::GetExtraStageInfoFromCourse( bool bExtra2, RString sPreferredG
 	}
 
 	pSongOut = pTrail->m_vEntries[0].pSong;
-	pStepsOut = pTrail->m_vEntries[0].pSteps;
+	pStepsOut = pTrail->m_vEntries[0].GetSteps();
 	return true;
 }