Fix things so `mkdir -p' can create very deep directories, e.g.,

Fix things so `mkdir -p' can create very deep directories, e.g.,
mkdir -p $(perl -e 'print "a/" x 40000') now works.

(main): For --parents (-p), call make_path with the
entire directory name, so we don't ever require that file operations
like stat or chmod be performed on the entire command line argument.