Avoid output messages size blow-up using huge bignums literals

libsolidity/ast/Types.h

@@ -437,6 +437,10 @@ private:
 
 	/// @returns true if the literal is a valid rational number.
 	static std::tuple<bool, rational> parseRational(std::string const& _value);
+
+	/// @returns a truncated readable representation of the bigint keeping only
+	/// up to 4 leading and 4 trailing digits.
+	static std::string bigintToString(dev::bigint const& num, bool _short);
 };
 
 /**