bug#31497: 27.0.50; vc-hg doesn't separate standard error from standard output

[Andrii Kolomoiets <andreyk.mad@gmail.com>]

Lars Ingebrigtsen writes:

>> $ hg log -l 1 -r . -T '{rev}'
>>
>> but that outputs
>>
>> not trusting file /tmp/hg/.hg/hgrc from untrusted user root, group root 
>> not trusting file /tmp/hg/.hg/hgrc from untrusted user root, group root
>
> filter out the "not trusting" lines, or is this just one of a
> gazillion error messages that can be output here?

Other errors also printed to stderr, so filtering out stderr completely
can hide meaningful errors.

This particular warning is also present in log and annotate buffers and
completely messing up vc-dir buffer.

There are option 'ui.report_untrusted' in hg since this commit:
https://www.mercurial-scm.org/repo/hg/rev/97369f6a6bb6

It present in mercurial 2.6.2, the earliest version I found in pip.

To filter out just "not trusting" warning I can propose to run hg like
this:
hg log --config ui.report_untrusted=0 -l 1 -r . -T '{rev}'

or specify '--config ui.report_untrusted=0' as default value for
vc-hg-global-switches

I think 'pull' and 'push' are the only commands that must print this
warning.