Fix Issue 669: Check that output and info files in load-into-counting.py are writable before loading input

[x] Is it mergable?
[x] Did it pass the tests?
[?] If it introduces new functionality in scripts/ is it tested?
  Check for code coverage.
[x] Is it well formatted? Look at `make pep8`, `make diff_pylint_report`,
  `make cppcheck`, and `make doc` output. Use `make format` and manual fixing as needed.
[x] Is it documented in the ChangeLog?
[x ] Was a spellchecker run on the source code and documentation after
  changes were made?