Fix globbing of filenames that contain special glob characters

[earthman1]

When specifying a coverage filename using the COVERAGE_FILE environment variable, special characters are not handled correctly. I use that facility to set the name of the coverage file to match the name of the test that I am running in pytest, so that I can associate the coverage with the specific test that generated that coverage. Some test names contain brackets, so the name of the test might be exampletest[b-a], and I transform that name into .coverage.exampletest[b-a] and then run

COVERAGE_FILE=.coverage.exampletest[b-a] pytest --cov "exampletest[b-a]"

Which results in the error:

re.error: bad character range b-a at position 5

Any special characters in a filename specified for creating a new file should be escaped before globbing for similar filenames.