Add AICurlInterface::getNumHTTPRunning

Replaces LLTextureFetch::getNumHTTPRequests.
Returns AICurlInterface::Stats::running_handles.
This is work in progress that temporarily doesn't compile because
LLTextureFetch::getNumHTTPRequests is still being used somewhere.

indra/newview/llviewertexturelist.cpp

@@ -1340,6 +1340,7 @@ void LLViewerTextureList::receiveImageHeader(LLMessageSystem *msg, void **user_d
 	{
 		received_size = msg->getReceiveSize() ;		
 	}
+	// Only used for statistics and texture console.
 	gTextureList.sTextureBits += received_size * 8;
 	gTextureList.sTexturePackets++;