Set a user-agent for curl isnewer

Fix sync warning about checking update failed due to rejected
connection without a user-agent on some mirrors.

The user-agent for curl isnewer is conform https://trac.macports.org/ticket/40319.

Closes: https://trac.macports.org/ticket/70973

src/pextlib1.0/curl.c

@@ -836,6 +836,7 @@ CurlIsNewerCmd(Tcl_Interp* interp, int objc, Tcl_Obj* const objv[])
  CURLcode theCurlCode;
  long theModDate;
  long userModDate;
+ const char* userAgent = PACKAGE_NAME "/" PACKAGE_VERSION " libcurl/" LIBCURL_VERSION;
 
  optioncrsr = 2;
  lastoption = objc - 3;
@@ -906,6 +907,13 @@ CurlIsNewerCmd(Tcl_Interp* interp, int objc, Tcl_Obj* const objv[])
  break;
  }
 
+ /* -A option */
+ theCurlCode = curl_easy_setopt(theHandle, CURLOPT_USERAGENT, userAgent);
+ if (theCurlCode != CURLE_OK) {
+ theResult = SetResultFromCurlErrorCode(interp, theCurlCode);
+ break;
+ }
+
  /* --max-redirs option, same default as curl command line */
  theCurlCode = curl_easy_setopt(theHandle, CURLOPT_MAXREDIRS, 50);
  if (theCurlCode != CURLE_OK) {