Added support for warning about and skipping files.

Files that do not exist or user does not have read access to
are skipped and users are warned that the file is skipped.
does the chmod/access functions work with windows permissions as well?  The [docs](https://docs.python.org/2/library/os.html#os.chmod) explicitly call out `stat.S_IREAD` so I just want to double check here.