Closing the Command Prompt using the "x" button doesn't update shell history file

[Mitchell Hentges]

To reproduce the issue:
1. Run Cygwin.bat to open a Cygwin shell in the "Command Prompt" terminal
2. Run some command, such as "echo test"
3. Click the Windows "x" button in the top-right corner of the terminal

The terminal closes, but `$HOME/.bash_history` is not updated to include
the "echo test" command.
Interestingly, when using mintty, the shell history is indeed saved when
the "x" button is pressed.

-- 
Mitchell Hentges
Engineering Workflow
Mozilla