[krbdev.mit.edu #2040] implement draft-ietf-krb-wg-gssapi-cfx (AES etc for GSSAPI)

[Ken Raeburn]

SIZE_MAX breaks the OSF and IRIX builds too.
I'll be on campus in a little while, a generic default should be easy 
enough to whip up then, we shouldn't need Windows-specific versions.