Login crash bug fix.

XMLRPCResponder constructor was missing.
This fixes the following crash signature:

VIEWER      : 2012-12-12T14:25:13Z INFO("AppInit"): setStartupState: Startup state changing from STATE_LOGIN_NO_DATA_YET to STATE_LOGIN_DOWNLOADING
VIEWER      : 2012-12-12T14:25:14Z INFO("AppInit"): transferRate: Buffer size:   1308 B
VIEWER      : 2012-12-12T14:25:14Z INFO("AppInit"): transferRate: Transfer rate: 11 kb/s

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff33df7f5 in XMLRPC_RequestGetData () from /usr/lib/x86_64-linux-gnu/libxmlrpc-epi.so.0
(gdb) bt

Reason was that if the server replied with some error code then
mResponse was undefined.

I also added code to retry three times in that case;
the http status code that I get was 503, which really
mean "Service *temporarily* unavailable", so a retry
is in order.

indra/newview/llxmlrpcresponder.h

@@ -99,6 +99,8 @@ private:
 	XMLRPC_REQUEST mResponse;
 
 public:
+	XMLRPCResponder(void) : mBufferSize(0), mReceivedHTTPHeader(false), mResponse(NULL) { }
+
 	// Accessors.
 	F64 transferRate(void) const;
 	bool is_downloading(void) const { return mReceivedHTTPHeader; }