Fail demonstrating nested form-fields
Fix PostBody::createMultipart()
Merge remote-tracking branch 'larowlan/multipart-forms' into fix-multipart-nested
Using the correct aggregation strategy when flattening

This change uses the query aggregator associated with the multi-part upload
object to ensure that the correct aggregation strategy is used when flattening
nested POST fields for a multi-part upload. Closes #690.