Require form-data on-demand, so that it doesn’t throw when not in use
Require form-data on-demand, so that it doesn’t throw when not in use

Fixes #933
craigspaeth/superagent,visionmedia/superagent,focusaurus/superagent,craigspaeth/superagent,fredigato/superagent,visionmedia/superagent,visionmedia/superagent,fredigato/superagent,focusaurus/superagent