allow ranked_symbol to be incremented

alib2data/src/common/ranked_symbol.hpp

@@ -80,6 +80,12 @@ public:
 	bool operator != ( const ranked_symbol & other ) const {
 		return compare ( other ) != 0;
 	}
+
+	ranked_symbol < SymbolType, RankType > & operator ++ ( ) {
+		++ m_symbol;
+
+		return *this;
+	}
 };
 template < class SymbolType, class RankType >