Add warning chevrons around the GC.Collect added to Warp3DImageModule in commit 5eb2526

Manually calling GC.Collect() really shouldnt' be necessary and is generally regarded as a bad idea.
A GC should occur anyway pretty shortly afterwards.
However, can leave this in development code for now to see if it does actually make a significant difference rather than simply doing a GC a little earlier.

OpenSim/Region/CoreModules/World/Warp3DMap/Warp3DImageModule.cs

@@ -208,6 +208,10 @@ namespace OpenSim.Region.CoreModules.World.Warp3DMap
                     bitmap = ImageUtils.ResizeImage(origBitmap, viewport.Width, viewport.Height);
             }
 
+            // XXX: It shouldn't really be necesary to force a GC here as one should occur anyway pretty shortly
+            // afterwards.  It's generally regarded as a bad idea to manually GC.  If Warp3D is using lots of memory
+            // then this may be some issue with the Warp3D code itself, though it's also quite possible that generating
+            // this map tile simply takes a lot of memory.
             GC.Collect();
             m_log.Debug("[WARP 3D IMAGE MODULE]: GC.Collect()");