This is an adopted version of 8b1e071d.
Since 1.7 has a flag to disable this behaviour, I think a better fix is
to disable this flag by default.

I actually applied the diff from
6904bb61e31595b70260840937114e79a646da5d in keyboard-shortcuts-plugin

... from
https://ajax.googleapis.com/ajax/libs/prototype/1.7.0.0/prototype.js

... from http://www.prototypejs.org/assets/2007/6/20/prototype.js