Merge branch 'ab/test-quoting-fix' into maint

Fixes for tests when the source directory has unusual characters in
its path, e.g. whitespaces, double-quotes, etc.
source: <redacted>

* ab/test-quoting-fix:
  config tests: fix harmless but broken "rm -r" cleanup
  test-lib.sh: fix prepend_var() quoting issue
  tests: add missing double quotes to included library paths

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