[PATCH 1 of 2 V3] patchbomb: includes series information in the header

[timeless at gmail.com]

You should fix the commit message too:
‎
We includes information about the series being patch bombed in all email. Two
new headers are added:

* X-Mercurial-Series-index: index of the patches in the series (starts at 1)
* X-Mercurial-Series-total: The total number of patches in the series

‎
+ msg['X-Mercurial-Series-Index'] = '%i' % idx
+ msg['X-Mercurial-Series-Total'] = '%i' % total
return msg, subj, ds‎