_Really_ don't report an error when cleaning already-deleted files.

My earlier #266 had a missing comma in the test that was giving false
results, so the code didn't actually work right.  Mea culpa.
Mark `cant_be_deleted?` as a private class method
Merge pull request #269 from randycoulman/really-clean-missing-files

Really don't report an error when cleaning already-deleted files
Add #269 to History
Fix infinite loop when cleaning files on windows

When checking if nonexistent file was deleted on windows the
tree-walking loop did not terminate properly.  Instead of checking for
no change for the path it looked for "." or "/", the latter of which
will not match a windows drive letter.

Now if the previous path is seen again the loop stops.
Update version for release