[dev] [surf] Scrolling with direction keys

I just updated webkit-gtk from 1.18 to 1.20, and now the direction
up / down keys select the next / previous link, rather than
scrolling up and down. I see now that surf advertises only Ctrl-K &
Ctrl-J scrolling, but I find the direction keys more comfortable.

Attached is a little patch restoring direction key scrolling.

For the record, I don't know about horizontal scrolling and the left
/ right keys; thankfully I don't come across sites which require it
often.

Nick