Search Builder - searching on email doesn't work with "IN" operator

To reproduce: in Search Builder, search on Email, using the "IN" operator. Input never validates.

In a previous patch (http://issues.civicrm.org/jira/browse/CRM-8548), the Search Builder "IN" operator was updated to broaden the range of regular expressions it would accept as valid. However, there is really no need for any validation at all, aside from making sure that the input is enclosed by parentheses. (And, in the future, we should consider removing the requirement for parentheses too. There's no reason for it.)

A patch is included. I also made the error messages more consistent and cleaned up the code a tiny bit.