Before, KeyError was caught at changeset_templater._show(), which said "no
key named '%s'" as it was intended to catch the KeyError of unknown map key.
Instead, we should catch KeyError explicitly for better error indication.
For those who don't know what the template engine is (read "everyone"), it is
hidden extension feature that allows switching template syntax in map file.
See b901d7e82888 for details.
We were assuming everything under 128 was printable ascii, but there are a lot
of control characters in that range that can't simply be included in json and
other targets. We forcibly encode everything under 32, because they are either
control char or oddly printable (like tab or line ending).
We also add the hypothesis-powered test that caught this.
The {parents} template is cumbersome for some uses, as it does not show
anything if there's only one "natural" parent and you can't use it to get the
full 40 digit node hashes for parents unless you rely on the behavior of
the --debug flag.
Introduce four new template keywords: {parent1}, {parent2}, {parent1node} and
{parent2node}. The "node" flavors of these always show full 40 digit hashes,
but users can get the short version with a filter construction like
'{parent1node|short}'.
Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.