Print info in texture console about curl request queuing

This includes also non-texture requests (not sure if it's worth it to
explicitely separate this data for just textures).

The texture console now prints: HTTP:c/q/a/r
Where, c = number of 'add' request commands in the command queue
(minus the number of 'remove' request in the command queue and not
taking into account the command_being_processed, nor entirely being
thread-safe with regard to adding requests to 'q' or 'a' next: it is
possible that a request is no longer counted in 'c' but not yet is added
to 'q' or 'a'.
q = number of queued (throttled) requests (by the curl thread).
a = number of actually added requests (to the multi handle).
r = last returned value of 'running handles' by libcurl.

Obviously, c and q should be small (0 or 1) most of the time and a and r
should be equal and maxed out. This turns out to be the case.

indra/llmessage/aicurlthread.cpp

@@ -2505,5 +2505,23 @@ bool handleNoVerifySSLCert(LLSD const& newvalue)
   return true;
 }
 
+U32 getNumHTTPCommands(void)
+{
+  using namespace AICurlPrivate;
+
+  command_queue_rat command_queue_r(command_queue);
+  return command_queue_r->size;
+}
+
+U32 getNumHTTPQueued(void)
+{
+  return AIPerHostRequestQueue::total_queued_size();
+}
+
+U32 getNumHTTPAdded(void)
+{
+  return AICurlPrivate::curlthread::MultiHandle::total_added_size();
+}
+
 } // namespace AICurlInterface