[krbdev.mit.edu #7013] looping detected in init_creds_step_request()

[Kevin Wasserman via RT]

...when krb5_get_init_creds_password() is invoked for a prinicpal that requires 
preauthentication and only supports weak crypto (and allow_weak_crypto 
is not specified).  It should fail, clearly, but probably in some speedier 
and more comprehensible fashion.

-Kevin Wasserman