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.
