Set CURLOPT_FORBID_REUSE for XMLRPCResponder

XMLRPCResponder is used to login, which is a HTTP 1.0 server
that doesn't support reuse of connections.
It's cleaner to close connections from our side too.

This changes,
0x7fffdcf93700   CURLIO      0x7fffcd86db40   * Connection #0 to host login.agni.lindenlab.com left intact
into
0x7fffdcf93700   CURLIO      0x7fffcd8b0bd0   * Closing connection #0

indra/llmessage/aicurl.cpp

@@ -1392,6 +1392,10 @@ void BufferedCurlEasyRequest::prepRequest(AICurlEasyRequest_wat& curl_easy_reque
 	// to id.secondlife.com for marketplace.secondlife.com.
 	allow_cookies = true;
   }
+  if (responder->forbidReuse())
+  {
+	curl_easy_request_w->setopt(CURLOPT_FORBID_REUSE, 1);
+  }
   if (allow_cookies)
   {
 	// Given an empty or non-existing file or by passing the empty string (""),

indra/llmessage/llhttpclient.h

@@ -217,6 +217,10 @@ public:
 		// Derived classes that implement completed_headers()/completedHeaders() should return true here.
 		virtual bool needsHeaders(void) const { return false; }
 
+		// A derived class should return true if curl should close the connection when done.
+		// The default is to keep connections open for possible reuse.
+		virtual bool forbidReuse(void) const { return false; }
+
 		// A derived class should return true if curl should follow redirections.
 		// The default is not to follow redirections.
 		virtual bool followRedir(void) const { return false; }

indra/newview/llxmlrpcresponder.h

@@ -107,6 +107,7 @@ public:
 	LLXMLRPCValue responseValue(void) const;
 
 	/*virtual*/ bool needsHeaders(void) const { return true; }
+	/*virtual*/ bool forbidReuse(void) const { return true; }
 	/*virtual*/ void received_HTTP_header(void) { mReceivedHTTPHeader = true; LLHTTPClient::ResponderBase::received_HTTP_header(); }
 	/*virtual*/ void completed_headers(U32 status, std::string const& reason, AITransferInfo* info);
 	/*virtual*/ void completedRaw(U32 status, std::string const& reason, LLChannelDescriptors const& channels, buffer_ptr_t const& buffer);