Notify the user of the outcome of mkdir in the case of a Time of Check Time of
Use attack on the parent directories to be created.

Also, converted the permissions arguments to our octal literals.
Copy paste error correct.  Sigh.
Merge pull request #442 from lydia-duncan/addMkdirSecurityNote

Add mkdir security note and octal literal default permissions [trivial]

Notify the user of the outcome of mkdir in the case of a Time of Check Time of
Use attack on the parent directories to be created.

Also, converted the permissions arguments to our octal literals.