Remove duplicate coverage files, favoring the file with higher coverage.
Change source_file_pathname stub return from cf*.gcno to class*.m
Use 'Slather::CoverageFile' instead of 'coverage_file_class' for 'dedupe' spec.
Make 'dedupe' more Ruby-ish
Merge pull request #16 from venmo/ayanonagon/dedupe

Remove duplicate coverage files, favoring the file with higher coverage.