Formvalid: focus field in error on error message link click

When one of the .errorContainer links is clicked, this will scroll to the field in error and give focus to the input element (requested in #1018).

1. Update `.errorContainer a` click handler with v3.1 code where appropriate.
2. Remove preIE7 conditional check as all browsers benefit from this.

**Note:** this does not need to be merged with master.