contrib/plan9/9mail

dagop: extract DAG local heads functionality from revlog

As part of implementing an alternate storage backend, I found myself
having to reimplement this function.

The DAG traversal logic is generic and can be factored out into a
standalone function.

We could probably combine this with headrevs(). But I'll leave that
for another time.

Differential Revision: https://phab.mercurial-scm.org/D4795

#!/bin/rc
# 9mail - Mercurial email wrapper for upas/marshal

fn usage {
	echo >[1=2] usage: mercurial/9mail -f from to [cc]
	exit usage
}

from=()
cc=()
to=()

switch($1){
case -f
	from=$2
case *
	usage
}

to=($3)
if(~ $#* 4)
	cc=(-C $4)

upasname=$from
upas/marshal $cc $to