pager: add tests
We've never had tests for pager, and I want to start experimenting
with ways to clean up the implementation and make it a bit more
graceful.
#require test-repo
$ cd "$TESTDIR"/..
New errors are not allowed. Warnings are strongly discouraged.
$ hg files "set:(**.py or **.txt) - tests/**" | sed 's|\\|/|g' |
> python contrib/check-config.py