Partial fix for #862 (Slow system menu in IE in XP). This fix cuts the freeze time...

Partial fix for #862 (Slow system menu in IE in XP). This fix cuts the freeze time down from over 10 seconds to about 2 or 3. Not quite sure why its still 2 to 3, but this is certainly better than what it was. To fix this, watchDog is instructed to use a minimum timeout if it is found to be in a system menu mode (according to GUIThreadInfo) and the window class of the focus object is not #32768 -- meaning that the focus in NVDA hasn't yet hit the menu.