[FIX] use matching operator to get patner from email in mail_thread.
The current operator is ilike but it add wildcards around right criteria so we can have false positive.

eg I'v got an email in my customer base like a_mail@provider.com

If I recive a mail from mail@provider.com as ilike operator uses wildcards a_mail@provider.com can potentially be matched.
Merge pull request #16 from nbessi/ocb_fix_856

[FIX] use matching operator to get patner from email in mail_thread.