Unclear (and badly reused) string on the sign-up form.

Steps to reproduce:

1. Create a user account with email address test@example.com.
2. Ensure email-based self-registration is enabled in your site.
3. Log out, and try to create a new account with email test@example.com

Actual result: you get the validation error: "This email address is already registered. New password?"

This just got flagged up by a confused user.

Better would be: "This email address is already registered. Perhaps you created an account in the past? Recover forgotten username or password"