Export logic of get_trust_pw() to new function get_trust_pw_clear().

Export logic of get_trust_pw() to new function get_trust_pw_clear().

get_trust_pw() just now computes the md4 hash of the result of
get_trust_pw_clear() if that was successful. As a last resort,
in the non-trusted-domain-situation, get_trust_pw() now tries to
directly obtain the hashed version of the password out of secrets.tdb.

Michael