[krbdev.mit.edu #7642] Can't get initial creds with empty password via API

[Greg Hudson via RT]

Passing an empty password to krb5_get_init_creds_password or 
krb5_init_creds_set_password doesn't not work; it is treated the same as 
an unspecified password.  See also:

http://mailman.mit.edu/pipermail/krbdev/2013-May/011525.html
https://bugzilla.redhat.com/show_bug.cgi?id=960001#c1