Cryptomount enhancements: detached headers, key-files and plain mode

[John Lane]

These patches provide extensions to the "cryptomount" command. There are four 
patches:

1. Support LUKS detached headers so that the header can be separated from the 
data payload, e.g. by storing on external removable media such as a USB key.

2. Support key files so that passphrase entry can be suppressed. The passphrase 
can be stored in a "key file" that can be stored, for example, on external 
removable media such as a USB key.

3. Support plain dm-crypt mode. Allow plain volumes to be opened. This is 
largely a re-factoring of exisitng code to allow the crypto routines be used 
independently of LUKS.

4. Support for hyphens in UUID. The "-u" option of cryptomount accepts a UUID. 
This option allows that to be delimited with hyphens so that the same format 
can be given to Grub as is passed to the Linux kernel boot options.

I can supply more information as required in reply to the individual patches.