Email validation conforming RFC 2822 (i.e. User Name <email@somedomain.tld>).
This function is originaly created by Cal Henderson <cal@iamcal.com>. Light modification made to accomodate "John Smith <js@jstest.com>" format (as describerd in 2822). You can find the original at http://www.iamcal.com/publish/articles/php/parsing_email/