StringToDifficulty->BackwardCompatibleStringToDifficulty. Don't accept song file backward compatible names other places, like in metrics

stepmania/src/Difficulty.cpp

@@ -42,7 +42,7 @@ LuaFunction( DifficultyDisplayTypeToLocalizedString, DifficultyDisplayTypeToLoca
 /* TODO: Format specific hacks should be moved into the file loader for 
  * that format.  We don't want to carry these hacks forward to file
  * formats that don't need them. */
-Difficulty StringToDifficulty( const RString& sDC )
+Difficulty BackwardCompatibleStringToDifficulty( const RString& sDC )
 {
 	RString s2 = sDC;
 	s2.MakeLower();

stepmania/src/Difficulty.h

@@ -22,6 +22,8 @@ const RString& DifficultyToString( Difficulty dc );
 Difficulty StringToDifficulty( const RString& sDC );
 LuaDeclareType( Difficulty );
 
+Difficulty BackwardCompatibleStringToDifficulty( const RString& sDC );
+
 typedef Difficulty CourseDifficulty;
 const int NUM_CourseDifficulty = NUM_Difficulty;
 #define FOREACH_ShownCourseDifficulty( cd ) for( Difficulty cd=GetNextShownCourseDifficulty((CourseDifficulty)-1); cd!=Difficulty_Invalid; cd=GetNextShownCourseDifficulty(cd) )
@@ -31,6 +33,7 @@ const RString& CourseDifficultyToLocalizedString( Difficulty dc );
 Difficulty GetNextShownCourseDifficulty( Difficulty pn );
 
 
+
 enum DifficultyDisplayType	// ID for coloring and localized strings in StepsDisplay 
 {
 	DifficultyDisplayType_Single_Beginner,

stepmania/src/NotesLoaderDWI.cpp

@@ -173,7 +173,7 @@ static bool LoadFromDWITokens(
 	int iNumFeet = atoi(sNumFeet);
 	// out.SetDescription(sDescription); // Don't put garbage in the description.
 	out.SetMeter(iNumFeet);
-	out.SetDifficulty( StringToDifficulty(sDescription) );
+	out.SetDifficulty( BackwardCompatibleStringToDifficulty(sDescription) );
 
 	NoteData newNoteData;
 	newNoteData.SetNumTracks( g_mapDanceNoteToNoteDataColumn.size() );

stepmania/src/NotesLoaderSM.cpp

@@ -34,7 +34,7 @@ static void LoadFromSMTokens(
 
 	out.m_StepsType = GameManager::StringToStepsType( sStepsType );
 	out.SetDescription( sDescription );
-	out.SetDifficulty( StringToDifficulty(sDifficulty) );
+	out.SetDifficulty( BackwardCompatibleStringToDifficulty(sDifficulty) );
 
 	// HACK:  We used to store SMANIAC as Difficulty_Hard with special description.
 	// Now, it has its own Difficulty_Challenge