fix; name regex failure

For reference:
https://github.com/felixge/node-formidable/blob/b268727a5494cbe499a594c7557c002917ac2e79/lib/incoming_form.js#L342
Merge pull request #25 from wavded/patch-1

fix; name regex failure
Only list irregular header names
Remove instanceof checks
Expose utils.callApp for testing

Fixes #26
Fix typo