Investigate why FileNotFoundError not captured when escalate mode is off

[lmmx]

The test test_parse_file_deleted in parse_test.py initially was written with a conditional block splitting on escalate, like the preceding test test_parse_file_error, but I then discovered that it doesn't respect the flag, and raises an error regardless.

[lmmx]

I commented this code out rather than delete it, for reference if this gets resolved in future and wants a test for the non-escalating case:

mvdef/tests/parse_test.py

Lines 110 to 115 in b031b78

	# TODO: fix #48
	# parsed = parse_file(p, escalate=escalate)
	# assert parsed is None
	# captured = capsys.readouterr()
	# stderr_cut = captured.err.split(":", 1)[1]
	# assert stderr_cut == "" # stored_error