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
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1