[#33948] fix email validation, allowing email with new domain name extension

J2.5 email addresses with new TLD extensions are not valid upon installation

#### Steps to reproduce the issue
1. Install a new site with Joomla! 2.5.x (I believe it is in all versions). 
2. Provide an admin email address with a new type of extension (e.g. .ninja .expert .company .cool .sexy etc.)
3. Test also any kind of email following these rules:

 The local part of an email (text before the "@") may include any of the following characters
 Uppercase and lowercase English letters (a–z, A–Z)
 Digits 0 to 9 
 These special characters: ! # $ % & ’ * + - / = ? ^ _ ` { | } ~
 Character . (dot, period, full stop) (ASCII: 46) provided that it is not the first or last character, and provided also that it does not appear consecutively (e.g. John..Doe@example.com is not allowed).



#### Expected result

Any email address from current and scheduled domain name should be accepted.

#### Actual result

Address is not accepted as valid.

#### System information (as much as possible)

Initial report on Joomla 2.5.20 - confirmed in 2.5.28-dev

#### Additional comments
Initial issue Submitted By: Ben Shomer - Open Date: 2014-07-14
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33948
fix email validation, allowing email with new domain name extension (more than 4 characters) like new gTLDs
- Adding more test instructions from Jean-Marie https://github.com/joomla/joomla-cms/pull/4899#issue-46596542