Failed signup forms don't perform a new ALTCHA

[Floppy]

1. Go to sign up
2. Enter a bad password or other invalid data and submit
3. Correct the highlighted form errors and resubmit

At this point the form is redisplayed with the ALTCHA verification failed banner message, and data entered into the form is lost.

This is only resolvable by fully reloading the signup page after a failure.