[BUG?] gitweb search fails with non-ascii characters

Easiest way to trigger this is by putting á in the commit search box and
then hitting enter. On git.kernel.org you get a 403 Forbidden. On
gitweb.samba.org it works. I know that git.kernel.org is non-standard,
but I can reproduce locally when I run instaweb (I think my system could
be mis-configured though).

Even odder, in all cases the letter in the search box becomes mangled on
the results page. Meaning searching again by hitting enter will not be
the same (and actually makes the search box text even worse).