Plumbing: Attempt at fixing the Cygwin missing std::to_string function.

src/text.h

@@ -76,7 +76,7 @@ template<typename T>
 const std::string format (int fmt_num, const std::string& fmt, T arg)
 {
     std::string output = fmt;
-    replace_positional (output, "{" + std::to_string(fmt_num) + "}", format (arg));
+    replace_positional (output, "{" + format (fmt_num) + "}", format (arg));
     return output;
 }