hgweb: set variables in qsparams
We currently mutate wsgireq.form in a few places. Since it is
independent from req.qsparams, we will need to make changes on
req.qsparams as well before consumers can use qsparams. So let's
do that.
Eventually, we'll delete wsgireq.form and all references to it.
Differential Revision: https://phab.mercurial-scm.org/D2780
#require docutils gettext
$ $TESTDIR/check-gendoc zh_TW
checking for parse errors