#11 ESC allows to quit

[Mateusz Viste]

Each time I use hexcompare, I notice I spontaneously hit 'ESC' when I want to quit, only to remember half a second later that I have to press 'q'. I believe I'm no special case, so there are probably more people with the same reflex.

Here is a patch that makes hexcompare quit both using 'q' and ESC.

[Mateusz Viste]

applied to upstream.