clean up Course cache logic

stepmania/src/Song.cpp

@@ -86,7 +86,9 @@ Song::~Song()
 	m_vpSteps.clear();
 
 	/* We deleted some Steps*; clear stuff that used it. */
-	SONGMAN->FlushCaches();
+	/* Don't make Song depend on SongManager.  It's leading to some 
+	 * confusing limitation on what can be done in SONGMAN->FlushCaches(). */
+	SONGMAN->Invalidate( this );
 }
 
 /* Reset to an empty song. */
@@ -103,7 +105,7 @@ void Song::Reset()
 
 	/* Courses cache Notes* pointers.  On the off chance that this isn't the last
 	 * thing this screen does, clear that cache. */
-	SONGMAN->FlushCaches();
+	SONGMAN->Invalidate( this );
 }
 
 
@@ -348,7 +350,7 @@ void Song::RevertFromDisk( bool bAllowNotesLoss )
 		}
 	}
 
-	StepsID::FlushCache();
+	StepsID::Invalidate( this );
 }