rails/rails — pull request #9745 by madmax (2013-03-16 14:39:14+00:00)
Title: Allow pass multipart option to form_for

Currently in Rails 4 form_for will ignore html: { multipart: true }
To add multipart you need have at last one f.file_field or f.multipart = true (this is so ugly!)

This change will revert posibility to pass multipart as html option