epee: fix peer ids being truncated on display

contrib/epee/include/string_tools.h

@@ -188,8 +188,10 @@ POP_WARNINGS
 		return boost::lexical_cast<std::string>(val);
 	}
 	//----------------------------------------------------------------------------
-	inline std::string to_string_hex(uint32_t val)
+	template<typename T>
+	inline std::string to_string_hex(const T &val)
 	{
+		static_assert(std::is_arithmetic<T>::value, "only arithmetic types");
 		std::stringstream ss;
 		ss << std::hex << val;
 		std::string s;