MFC of the following:

MFC of the following:

- sys/modules/md/Makefile rev 1.14:

  Rename GEOM class kernel module g_md.ko to geom_md.ko for
  consistency with the rest.  The g_md.ko is now a hardlink of
  geom_md.ko for backward compatibility.

- sys/sys/mdioctl.h rev 1.21:

  Removed (now unused) #define.

- sys/boot/forth/loader.conf rev 1.102:

  Add more GEOM classes to defaults/loader.conf. Add references to
  manual pages to those already present.

- sbin/mdconfig/mdconfig.c rev 1.45:

  Simplify mdmaybeload() function.

Reviewed by:	ru and pjd
Approved by:	re (kensmith)