A little explanation of what the patch does; most of the code in this
patch already existed.

I extracted the in-line code from "luks.c" that creates the crypto disk
into a new cryptomount function called "grub_cryptodisk_create" that is
then used by the luks module and is also avilable to the cryptomount
module.

I extracted the "set_passphrase" function from the "devmapper.c"
committed (e7f405ab) in the "peter/devmapper" branch so that I could use
it in cryptomount to hash a manually entered passphrase.

I then wrote some additional options and a small block of code to
implement plain mode using the above.