WinHugs patch, machdep.c

Hi, Patch for machdep.c. This removes the feature where the cursor changes to the rubbish bin during garbage collection. I've never seen this in action, which probably means that it either didn't work, or that on a modern machine GC is too fast to spot it. Either way, a garbage can on windows means delete files, not freeing memory! Also instead of destroying the main window with windows API calls and the magic hWndMain in response to exit, be nice and call WinHugsExit. WinHugs.patch renames this call from KillWindow to WinHugsExit and adds it to the appropriate header. Thanks Neil