tests/make: add a few more tests, mainly for special targets

make(1): update and add comments in tests

As a result of the new comments, some line numbers have changed in the
output of the tests. No other changes.

make(1): describe the purpose of each newly added unit test dummy

make(1): add dummies for fine-grained tests, one per single feature

The test names have been derived from the current manual page.

All these tests are dummies right now, and the code from the existing
tests will be moved into the new tests step by step.

This is done to prevent modmisc, escape, varmod-edge and varmisc from
growing without any bounds, and to reduce the side-effects of one test
to the others.