[churn] Ignore merge csets
Merge changesets attributed a large number of lines to people that didn't
actually develop it, but simply merged the code. By ignoring merges, we get
a more accurate picture of how much code everyone changed.
#header#
# HG changeset patch
# User #author#
# Date #date|hgdate#
# Node ID #node#
#parent%changesetparent#
#desc#
#diff#