Patch to use imap_root before imap connect (significant speedup)

[ziba]

By communicating the roundcube imap_root preference to iloha imap before connecting to imap, we can take advantage of iloha's ability to skip the namespace discovery phase.

In an environment like ours (80K users, 900K mailboxes), this cuts the time it takes the backend to load a single email message from ~1.7 seconds to ~0.2 seconds (on an unloaded test system).

Please let me know if I can change anything to make this patch more acceptable. Thanks.

[maharaja]

two things

# if rcmail::get_instance()->config->get('imap_root') gives an empty string, the patch renders roundcube unusable. # normally i am against the usage of globals in such a way. but this is better than nothing :)

[maharaja]

updated patch

[ziba]

v2 is missing a semicolon