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

[Ken Raeburn via RT]

Oops.  SIZE_MAX is a C99 addition, defined in stdint.h.  I should check 
whether Windows and other platforms have it, or if a default is 
needed...  It's the limit of size_t, like LONG_MAX is for long.

Ken