Start making edge of tabs slightly curvier

Aiming to duplicate what chrome has done without actually
looking at the source, which is *probably* a bad idea.

Also changed the border of the tab to something slightly
less hideously solid black.
Attempt to fallback decode as ASCII

In general everything *should* be valid Unicode since ascii is
a subset of UTF8, but it's entirely possible that something weird
is going on that I don't fully understand yet.

This seems to happen most when I'm on the shitty SFwireless.org
network near the front of 4B.