Added calls to GC.AddMemoryPressure() when unmanaged memory is allocated for ODE (helps the GC make better scheduling choices), and a call to GC.Collect() right before logins are enabled for a region. Although this doesn't change actual memory usage, it improves the reported usage from OpenSim and the operating system

OpenSim/Region/Framework/Scenes/Scene.cs

@@ -1107,6 +1107,11 @@ namespace OpenSim.Region.Framework.Scenes
                     }
                     if (loginsdisabled && (m_frame > 20))
                     {
+                        // In 99.9% of cases it is a bad idea to manually force garbage collection. However,
+                        // this is a rare case where we know we have just went through a long cycle of heap
+                        // allocations, and there is no more work to be done until someone logs in
+                        GC.Collect();
+
                         m_log.Debug("[REGION]: Enabling Logins");
                         loginsdisabled = false;
                     }