Screen update when running call-process

[Lennart Borgman]

I noticed a strange thing when I was running a subprocess with screen 
update. I started it with

       (setq sts (call-process "sh" nil (current-buffer) t "-c" "make")))))

The t means 'update display'. That works nicely as long as I do not 
switch frame or switch to another app. When I get back the screen is no 
longer updated. This is on w32 (in case anyone would doubt;-)

I suppose this is problem in the w32 *.c files, but I would be glad if 
you could test on other platforms.