Update to r41912:
Make section IDs in GEOM chapter lowercase, and adjust references to them
from other parts of the book.

Submitted by:	Bjoern Heidotting
Obtained from:	The FreeBSD German Documentation Project


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45675 c2e8774f-c49f-e111-b436-862b2bbc8956