magic.h, etc.: Rename the transform capability bits.

Mostly mechanical, with the following rune:

	git grep -zil TRANSFORMNUM | xargs -0r sed -i '
		s/TRANSFORMNUM/BIT/g
		s/transformnum/bit/g
		s/BIT_ANCIENT/&TRANSFORM/g'

But I renamed the `capab_transformnum' member of `struct msg' back by
hand, because it's referring specifically to a selected
transform.  (This will make sense later.)

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>