Add fu->redirect, change $st->row behavior on 0 results, minor fixes

And with this, I have a working rewrite of the manned.org backend into
FU. \o/

The $st->row methods are very useful even for queries that may not
return anything, so their old behavior was unhelpful. Interestingly
enough, the error-on-multiple-rows did catch an actual bug in
Manned.org, so I'm keeping that behavior.

FU/SQL.pm

@@ -51,7 +51,7 @@ sub VALUES {
     : SQL 'VALUES (', COMMA(@_), ')';
 }
 
-sub IN($a) {
+sub IN :prototype($) ($a) {
     confess "Expected arrayref" if ref $a ne 'ARRAY';
     bless \$a, 'FU::SQL::in'
 }