Sign Up: mistakes in error message for existing Email in English

Steps to reproduce:

1. Open the page http://qa.jtalks.org/jcommune/
2. Select English localization
3. Click on "Sign Up" button
4. Enter the registered Email into "Email" field (for ex. admin@jtalks.org)
5. Submit the form by clicking "Sign Up" button or pressing Enter key
6. Overview error message text under "Email" field
   Actual result:
   Error message "User with the email already exists." is shown
   Expected result:
   Error message "User with this email already exists" is shown

Reproduced also on Sign Up page http://qa.jtalks.org/jcommune/user/new