note 31368 deleted from function.mkdir by aidan

Note Submitter: cgibbard ---- I'd just like to make the comment that the use of the word "subtracted" with respect to umasks is not incorrect. The subtraction is simply not occurring over the integers which is what caused the confusion. Think of it as set subtraction or bitfield subtraction, and you'll see that it's a perfectly good word to use. Thinking of the umask/permission bits as integers in the first place is the strange part. They can be viewed as integers, (as can jpeg images, or executable programs) but the more natural idea is that they're sets or bitfields.