I reduced the memory requirements for test_counting_single.py
(Please ignore changes to test_save_load_merge, jlippy has fixed test_subset_graph.py)

Checklist:

• [ y ] Is it mergable
• [ y ] Did it pass the tests?
• [ no new functionality ] If it introduces new functionality in scripts/ is it tested?
  Check for code coverage.
• [ y ] Is it well formatted? Look at pep8/pylint, cppcheck, and
  make doc output. Use autopep8 and astyle -A10 --max-code-length=80
  if needed.
• [ y ] Is it documented in the Changelog?
• [ y ] Was spellcheck run on the source code and documentation after changes
  were made?