Error message field names should use label text, not raw field name

This causes the tests in test-validators to fail with 

    TypeError: Object #<Object> has no method 'labelText'
    at exports.matchValue (/Users/ryan.french/Documents/Code/RYFN/forms/lib/validators.js:46:44)

However, there is a labelText method available when in regular use - the `field` object has all the methods in `lib/fields.js`

What can I do to resolve this?
maybe we should put the default in a variable, since it's repeated twice?