config: guard against setconfig specifying unicode values on py3
This was leading to some difficult to trace problems because the
values were set in one place, but then blew up much later in the
program. Exploding violently with an assertion seems reasonable here.
Some Mercurial commands produce a lot of output, and Mercurial will
attempt to use a pager to make those commands more pleasant.
To set the pager that should be used, set the application variable::
[pager]
pager = less -FRX
If no pager is set, the pager extensions uses the environment variable
$PAGER. If neither pager.pager, nor $PAGER is set, a default pager
will be used, typically `more`.
You can disable the pager for certain commands by adding them to the
pager.ignore list::
[pager]
ignore = version, help, update
To ignore global commands like :hg:`version` or :hg:`help`, you have
to specify them in your user configuration file.
To control whether the pager is used at all for an individual command,
you can use --pager=<value>::
- use as needed: `auto`.
- require the pager: `yes` or `on`.
- suppress the pager: `no` or `off` (any unrecognized value
will also work).
To globally turn off all attempts to use a pager, set::
[pager]
enable = false
which will prevent the pager from running.