Fixed exception when files were updated while script was running.

m_UpdatedFiles was being updated while it was still being used by the
script thread.  Instead, copy the list, clear it out, and have the
script thread process the copy.

code/src/FileGroupTab.cs

@@ -571,10 +571,11 @@ namespace FileWatcher
 
             try
             {
-                updated(m_UpdatedFiles);
-
+                var updateFiles = m_UpdatedFiles;
                 m_UpdatedFiles.Clear();
 
+                updated(updateFiles);
+
                 Logger.Log("Just finished running '" + ScriptPath + "'");
 
                 Form1.Instance.notifyIcon1.ShowBalloonTip(500, "Script Ran", "Finished running '" + ScriptPath + "'", ToolTipIcon.Info);