Try to get heimdal working with HEAD.

Try to get heimdal working with HEAD.
- Provide generic functions for
  - get valid encryption types
  - free encryption types
- Add encryption type parm to generic function create_kerberos_key_from_string()
- Try to merge the two versions (between HEAD and SAMBA_3_0) of kerberos_verify.c

I think this should work for both MIT and heimdal, in HEAD.  If all goes smooth,
I'll move it over to 3.0 soon...
(This used to be commit 45e409fc8da9f26cf888e13d004392660d7c55d4)