Add a file for user warnings, userlog.txt. Until now, these types of warnings have either been cluttering info.txt or buried in log.txt where no sane user would want to look.

stepmania/src/StepMania.cpp

@@ -902,6 +902,7 @@ static void ApplyLogPreferences()
 	LOG->SetShowLogOutput( PREFSMAN->m_bShowLogOutput );
 	LOG->SetLogToDisk( PREFSMAN->m_bLogToDisk );
 	LOG->SetInfoToDisk( true );
+	LOG->SetUserLogToDisk( true );
 	LOG->SetFlushing( PREFSMAN->m_bForceLogFlush );
 	Checkpoints::LogCheckpoints( PREFSMAN->m_bLogCheckpoints );
 }