A simple testing framework

To run the tests, do:

cd tests/
./run-tests

This finds all scripts in the test directory named test-* and executes
them. The scripts can be either shell scripts or Python. Each test is
run in a temporary directory that is removed when the test is complete.

A test-<x> succeeds if the script returns success and its output
matches test-<x>.out. If the new output doesn't match, it is stored in
test-<x>.err.

There are some tricky points here that you should be aware of when
writing tests:

- hg commit and hg up -m want user interaction

  for commit use -m "text"
  for hg up -m, set HGMERGE to something noninteractive (like true or merge)

- changeset hashes will change based on user and date which make
  things like hg history output change

  use commit -m "test" -u test -d "0 0"

- diff will show the current time

  use hg diff | sed "s/\(\(---\|+++\) [^ \t]*\)[ \t].*/\1/" to strip
  dates

- set -x and pipelines don't generate stable output

  turn off set -x or break pipelines into pieces