fix error reporting

stepmania/src/RageFileDriver.h

@@ -21,6 +21,8 @@ public:
 	virtual void FlushDirCache( const CString &sPath );
 	virtual bool Remove( const CString &sPath ) { return false; }
 
+	/* Possible error returns from Open, in addition to standard errno.h values: */
+	enum { ERROR_WRITING_NOT_SUPPORTED = -1 };
 protected:
 	FilenameDB *FDB;
 };