Debug code bug fix; removal of CurlEasyHandle::getErrorString()

CurlEasyHandle::mErrorBuffer (CURLOPT_ERRORBUFFER) can NOT be
used to retrieve information about an error returned by
curl_multi_info_read in CURLMsg::data::result. This buffer is
only initialized when a curl_easy_* call returns an error,
and those errors are already printed automagically.

Initialize the buffer with an empty string upon invokation
of an curl_easy_* call, so we are sure the error belongs to
the last call.

indra/newview/llxmlrpctransaction.cpp

@@ -340,8 +340,8 @@ void LLXMLRPCTransaction::Impl::curlEasyRequestCallback(bool success)
 	if (result != CURLE_OK)
 	{
 		setCurlStatus(result);
-		llwarns << "LLXMLRPCTransaction CURL error "
-				<< mCurlCode << ": " << curlEasyRequest_w->getErrorString() << llendl;
+		llwarns << "LLXMLRPCTransaction CURL error: "
+				<< AICurlInterface::strerror(mCurlCode) << llendl;
 		llwarns << "LLXMLRPCTransaction request URI: "
 				<< mURI << llendl;