Merge branch 'es/test-cron-safety'

The test script had an incomplete and ineffective attempt to avoid
clobbering the testing user's real crontab (and its equivalents),
which has been completed.

* es/test-cron-safety:
  test-lib: fix non-functioning GIT_TEST_MAINT_SCHEDULER fallback

diff --cc t/test-lib.sh
Simple merge