Move frame loop entirely within Scene.Update() for better future performance analysis and stat accuracy.

Update() now accepts a frames parameter which can control the number of frames updated.
-1 will update until shutdown.
The watchdog updating moves above the maintc recalculation for any required sleep since it should be accounted for within the frame.

OpenSim/Framework/Util.cs

@@ -1753,6 +1753,20 @@ namespace OpenSim.Framework
         }
         const Int32 EnvironmentTickCountMask = 0x3fffffff;
 
+        /// <summary>
+        /// Environment.TickCount is an int but it counts all 32 bits so it goes positive
+        /// and negative every 24.9 days. Subtracts the passed value (previously fetched by
+        /// 'EnvironmentTickCount()') and accounts for any wrapping.
+        /// </summary>
+        /// <param name="newValue"></param>
+        /// <param name="prevValue"></param>
+        /// <returns>subtraction of passed prevValue from current Environment.TickCount</returns>
+        public static Int32 EnvironmentTickCountSubtract(Int32 newValue, Int32 prevValue)
+        {
+            Int32 diff = newValue - prevValue;
+            return (diff >= 0) ? diff : (diff + EnvironmentTickCountMask + 1);
+        }
+
         /// <summary>
         /// Environment.TickCount is an int but it counts all 32 bits so it goes positive
         /// and negative every 24.9 days. Subtracts the passed value (previously fetched by
@@ -1761,8 +1775,7 @@ namespace OpenSim.Framework
         /// <returns>subtraction of passed prevValue from current Environment.TickCount</returns>
         public static Int32 EnvironmentTickCountSubtract(Int32 prevValue)
         {
-            Int32 diff = EnvironmentTickCount() - prevValue;
-            return (diff >= 0) ? diff : (diff + EnvironmentTickCountMask + 1);
+            return EnvironmentTickCountSubtract(EnvironmentTickCount(), prevValue);
         }
 
         // Returns value of Tick Count A - TickCount B accounting for wrapping of TickCount