patchbomb: respect HGPLAIN when piping --test output to PAGER
It makes easy to use `hg email --test` from another tool.
#!/bin/sh
cat >> $HGRCPATH <<EOF
[extensions]
hgcia=
[hooks]
changegroup.cia = python:hgext.hgcia.hook
[cia]
user = testuser
project = testproject
test = True
EOF
hg init src
hg init cia
cd src
echo foo > foo
hg ci -Amfoo
hg push ../cia