add --plain option to patchbomb.
this omits the hg patch headers. it makes a patchbomb email look like
a regular email with a patch.
Metadata-Version: 1.0
Name: mercurial
Version: 0.7
Summary: scalable distributed SCM
Home-page: http://selenic.com/mercurial
Author: Matt Mackall
Author-email: mpm@selenic.com
License: GNU GPL
Description: UNKNOWN
Platform: UNKNOWN