Correct optimization from 3464f5e77f34; add a test.
If there are two (or more) heads that point to the same .hgtags
node, we can safely skip parsing the file in all but the last head.
(In 3464f5e77f34, we were parsing the file in the first head and
skipping all the others.)
#!/bin/sh
echo % init
hg init
echo % commit
echo 'a' > a
hg ci -A -m test -u nobody -d '1 0'
echo % annotate -c
hg annotate -c a
echo % annotate -d
hg annotate -d a
echo % annotate -n
hg annotate -n a
echo % annotate -u
hg annotate -u a
echo % annotate -cdnu
hg annotate -cdnu a
cat <<EOF >>a
a
a
EOF
hg ci -ma1 -d '1 0'
hg cp a b
hg ci -mb -d '1 0'
cat <<EOF >> b
b
b
b
EOF
hg ci -mb2 -d '2 0'
echo % annotate b
hg annotate b
echo % annotate -nf b
hg annotate -nf b
hg up -C 2
cat <<EOF >> b
b
c
b
EOF
hg ci -mb2.1 -d '2 0'
hg merge
hg ci -mmergeb -d '3 0'
echo % annotate after merge
hg annotate -nf b
hg up -C 1
hg cp a b
cat <<EOF > b
a
z
a
EOF
hg ci -mc -d '3 0'
hg merge
cat <<EOF >> b
b
c
b
EOF
echo d >> b
hg ci -mmerge2 -d '4 0'
echo % annotate after rename merge
hg annotate -nf b
echo % linkrev vs rev
hg annotate -r tip a