Enhance e107 to allow for third-party email address validation.

[CaMer0n]

Motivation

e107 currently uses simple email syntax validation, but is unable to check if an email address is deliverable, real or fake.

Proposed Solution

Allow plugin developers to override the check_email() function that is used throughout e107, in order to integrate with third-party solutions that can provide more extensive validation.

Example plugin usage (e_module.php)

e107::getOverride()->replace('check_email', 'myplugin_module::checkEmail');

class myplugin_module
{
        public static function checkEmail($email)
	{
		if(empty($email))
		{
			return false;
		}

		// run other checks. 

		// Valid email
		return $email;
	}
}