More frickle work for shifted keys.

Apparently, when a shifted key is pressed, GTK automatically
converts the keycode to upper case and removes the SHIFT modifier
necessary to type the key. Unfortunately, the key is registered
in the configuration with "<Shift>f", not "F", so it doesn't trigger
once configured.

git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@924 ef8490bc-f317-4725-81ed-e95a9aca1bcf