Hi again,

I realised I'd forgotten to add tests, and that made me realise that
url-query-allowed-chars is not correct for this, since that also
contains '=', '&', and ';'. So here's an updated patch, which creates a
new url-query-key-value-allowed-chars constant, which is
url-query-allowed-chars minus the aforementioned three chars, and adds
tests covering that, for both keys and values.

- ilmari