[horde] Getting user list when using IMP for authentication

[Aleksandar Milivojevic]

Unless I'm missing something, currently if I want to allow Horde to 
fetch list of users (needed for example for editing permissions in 
calendar, task list, and some other applications), I need to store Cyrus 
admin password into IMP's config file.

If I choose not to manage Cyrus users through Horde, it would be nice if 
I could choose some other backend for tasks that simply need to fetch 
the list of users.  For example, in my case Cyrus authenticates against 
LDAP, so if I could point Horde to fetch list of users directly from 
LDAP, it would be way more secure (for example, I could specify that DN 
Horde binds with has read-only access and limit that access even furter, 
instead of giving it full administrative access to my Cyrus IMAPD).