this is issue https://github.com/SiteSupport/gevent/issues/116

the mimetools Message class isn't of much help here, but replacing it
probably will do more harm than good. so, we parse multiline headers
on our own.

The
,----
| if 'bytearray' in __builtins__.__dict__:
`----
fails when running under py.test, so I replaced that too.