"ALT-F4" does not close terminal when using Command Prompt

[Mitchell Hentges]

To reproduce the issue:
1. Run Cygwin.bat to open a Cygwin shell in the "Command Prompt" terminal
2. Click the "ALT-F4" keyboard combination

The Cygwin terminal should close (ideally allowing the shell to do cleanup,
such as writing to its history file).
However, instead, a "ding" is sounded, but the terminal remains open.

-- 
Mitchell Hentges
Engineering Workflow
Mozilla