With Tk 8.5 the askpass utility can hang waiting for the wish shell
implicit event loop to exit. This patch uses an explicit event loop
to ensure correct application termination.
Reported-by: Anders Kaseorg <andersk@mit.edu> Tested-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>