[krbdev.mit.edu #7647] let ktutil support non-default salts

[Benjamin Kaduk via RT]

Adding an entry to a keytab from a password with ktutil currently assumes the default salt, 
without even the options for salt types that are available in kadmin.
It would be nice to have those, as well as the ability to specify an explicit salt string (or make an 
AS_REQ to get the actual salt for the principal from the KDC).
If random salts become more popular, this functionality will be more necessary than it presently 
is.