Resizing terminal window while in a pager confuses the next pager

[georgebrock]

1. Open gitsh in a small terminal emulator window
2. Run a command that starts a pager
3. Increase the window size
4. Close the pager
5. Run a command that starts a pager
6. The new pager will be initialised at the original smaller window size

This is similar to the issue discussed in #144 (comment) and fixed in #221.

We might be able to fix this by updating environment variables on SIGWINCH. The less(1) manual page says this about the COLUMNS environment variable:

Sets the number of columns on the screen. Takes precedence over the number of columns specified by the TERM variable. (But if you have a windowing system which supports TIOCGWINSZ or WIOCGETD, the window system's idea of the screen size takes precedence over the LINES and COLUMNS environment variables.)