[imp] TOS not work for Horde 3

[David Chang]

HI all:
Recently i noted that even TOS was actived in imp/config/prefs.php,but i still
can use any Horde's application if i reject TOS agreement.

Horde 3.0.4 + IMP H3 4.0.3
Horde authenaction backend:ldap
Set hordeauth=true to imp/config/server.php

David Chang