Change MAKE-DIRECTORY and DELETE-DIRECTORY to strip off any trailing

Change MAKE-DIRECTORY and DELETE-DIRECTORY to strip off any trailing
slash from the filename before giving it to the primitive.  Previously
these were forcing a trailing slash onto the filename.  Most unix
implementations don't care about this, but Linux rejects the old
behavior, and the new behavior is more "correct", in the sense that
this is an operation on the file that is the directory.