[imp] adding realm in IMP5

[Andrew Morgan]

Is there a recommended way to replicate/replace the old "realm" parameter 
in IMP5?  I have 2 issues I am trying to solve:

1. I have 8 different IMAP servers.  2 of them are different IMAP servers, 
but I want to share user preferences between them (we are migrating slowly 
over time from an old IMAP server to a new IMAP server)

2. Username is not unique between all 8 IMAP servers, so in the 
preferences backend (MySQL) I need to have a realm/domain appended to the 
username.  For example, pref_uid should contain "morgan at orst.edu" instead 
of "morgan".

In IMP4, I used the realm parameter to accomplish both goals.  I have been 
reading the backends.php and hooks.php files, but I don't see how to get a 
realm/domain appended to the pref_uid.

Thanks,
 	Andy