Bugfix: `getFormvalues` choked on >1 form with same field names.
If a document had more than one form, and there was overlap in field
names across forms, `getFormValues` would not return the correct result.
Solution is to pass formSelector to `getFieldValue` so it only attempts
to retrieve values for fields in the given form.
Merge pull request #376 from lukeasrodgers/bugfix_getFormValues_for_multiple_forms

Bugfix: `getFormvalues` choked on >1 form with same field names.