LDAP auto-completion (ticket #1483899)

Hi,

Since some people seem to be interested in LDAP autocompletion feature, (http://trac.roundcube.net/trac.cgi/ticket/1483899) I coded it on my RC copy. I tried it, and it looks like working ; (I permit myself to join the patch to this mail, because it is not really huge).

By the way, my current RC copy begins to be slightly different from the svn copy. So it will be great if some LDAP users could give some feedbacks. In addition, a main problem of this code is that it could certainly slow the generations of the pages in some cases. (I have less than 20 contacts on my LDAP, but what if there was more than a thousand ?).

best regards,