Fallback for updating account information.

I'll probably run into more of these, but I'm building a theme using the whole "progressive enhancement" ideology and that is including Javascript.

I'm trying to post account information to the user:account action but, presently, there is no way to save the posted information to the user model. That is only available with the user:on_update_account AJAX handler.

Anyway, this just checks to see if a form is being posted with a submit button name of "account_update" and executes that handler.

```<input type="submit" name="update_account" value="Save">```