Ensure the returnUrl is maintained on form errors for the registraton page.
Merge branch 'master' into keep-return-url-on-form-error
Merge branch 'master' into keep-return-url-on-form-error
Fixed the test  - render method takes an option string.
Merge pull request #5843 from guardian/keep-return-url-on-form-error

Keep returnUrl on form errors for the registration page