Print information about type of test and subdirectory before running tests.

Print information about type of test and subdirectory before running tests.

When testing check-world it's hard to know what the test the test failure
output belongs to. The tap test output is especially problematic, partially
due to our practice of reusing test names like 001_basic.pl.

This isn't a real issue on the buildfarm, which invokes tests separately, but
locally and for CI it's quite annoying.

To fix, the test target provisos in Makefile.global.in now output
  echo "+++ (regress|isolation|tap) [install-]check in $(subdir) +++"
before running the tests.

Discussion: https://postgr.es/m/20220330165039.3zseuiraxfjkksf5@alap3.anarazel.de