Use Environment.TickCount & Int32.MaxValue; instead of Util.EnvironmentTickCount(); when producing the threads report to reduce wraparound.

This matches the tickcount masking in the thread watchdog.
For some reason, Util.EnvironmentTickCount() masks ticks by 0x3fffffff instead of 0xffffffff

OpenSim/Framework/Servers/BaseOpenSimServer.cs

@@ -251,7 +251,7 @@ namespace OpenSim.Framework.Servers
 
             sb.Append(threads.Length + " threads are being tracked:" + Environment.NewLine);
 
-            int timeNow = Util.EnvironmentTickCount();
+            int timeNow = Environment.TickCount & Int32.MaxValue;
 
             sb.AppendFormat(reportFormat, "ID", "NAME", "LAST UPDATE (MS)", "LIFETIME (MS)", "PRIORITY", "STATE");
             sb.Append(Environment.NewLine);