optimized UnlockSystem::FindSong() function so its a O(log n) operation instead of O(n)

(improved from sequential to binary search; still may have bugs so old code is commented out)

stepmania/src/UnlockSystem.h

@@ -69,6 +69,8 @@ public:
 	float UnlockToasty();
 	bool RouletteUnlock( const Song *song );
 
+	void DebugPrint();
+
 private:
 	void SortSongEntriesArray();  // sorts unlocks
 	bool ParseRow(CString text, CString &type, float &qty, CString &songname);