Add inventory.<url>.RequestsMade stat.

This gives a count of all requests made to the remote inventory service.
This is finer grained than inventory.httpfetch.ProcessedFetchInventoryRequests since such a request can be comprised of many individual inv service calls.
In addition, this will count requests that don't go through the HTTP inventory fetch (e.g. HG, archiving, etc.)

prebuild.xml

@@ -823,6 +823,7 @@
       <Reference name="OpenSim.Capabilities"/>
       <Reference name="OpenSim.Framework.Communications"/>
       <Reference name="OpenSim.Framework.Console"/>
+      <Reference name="OpenSim.Framework.Monitoring"/>
       <Reference name="OpenSim.Framework.Servers.HttpServer"/>
       <Reference name="OpenSim.Region.Framework"/>
       <Reference name="OpenSim.Server.Base"/>