tests leave behind unremovable file.

After resolving #97 (i think), running the tests for directory leaves a file that cannot be removed except by root. This caused the hackage builder to stall for roughly a week because it was unable to remove the following file: `/home/builder/builder-dir/build-cache/tmp-install/directory-1.3.9.0/dist/test-RemovePathForcibly.tmp/removePathForcibly.tmp/f` It would be good if the test suite were fixed to avoid this issue.