[FIX] Validate email address input for customer registration

[Martin]

Further Modifications: Users can also enter an invalid email address when editing their account details. Based on Martin's instructions above, I made the following modifications.

STEP ONE: You'll be making most of the changes to the class.account.php file

Silly me, I assumed that Interspire wouldn't duplicate code for editing accounts into a whole other class but it appears I was wrong...

Thanks for catching that CF.. Much appreciated.