convert/gnuarch: retrieve known archive names list
This will make possible in a followup patch to prevent
following history that is not reachable because an archive
is unknown to the user.
#!/bin/sh
echo "[extensions]" >> $HGRCPATH
echo "color=" >> $HGRCPATH
hg init repo
cd repo
cat > a <<EOF
c
c
a
a
b
a
a
c
c
EOF
hg ci -Am adda
cat > a <<EOF
c
c
a
a
dd
a
a
c
c
EOF
echo '% default context'
hg diff --nodates --color=always
echo '% --unified=2'
hg diff --nodates -U 2 --color=always