[krbdev.mit.edu #959] dk_derive.c does not copy the enctype

[Greg Hudson via RT]

krb5int_derive_keyblock still doesn't set the enctype of the result 
keyblock, but none of its callers expect it to, so there shouldn't be any  
visible bugs as a result.  (I can't tell from the description in this 
issue what the original visible bug was, so I don't know what fixed it, 
but I'm pretty certain it's not present any more.)