mkdir cleanups: Let umask do its thing at the syscall level, have mode be a global...

mkdir cleanups: Let umask do its thing at the syscall level, have mode be a global to prepare for -m, use do_blah name loopfiles() usually calls, one less redundant mkdir() call, go ahead and modify writeable args instead of strdup(), return before restoring / so error message is better, use perror_msg().