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
hg init
echo foo > foo
hg add foo
hg commit -m1 -d"0 0"
echo "# should show copy"
hg copy foo bar
hg debugstate|grep '^copy'
echo "# shouldn't show copy"
hg commit -m2 -d"0 0"
hg debugstate|grep '^copy'
echo "# should match"
hg debugindex .hg/data/foo.i
hg debugrename bar
echo bleah > foo
echo quux > bar
hg commit -m3 -d"0 0"
echo "# should not be renamed"
hg debugrename bar
hg copy -f foo bar
echo "# should show copy"
hg debugstate|grep '^copy'
hg commit -m3 -d"0 0"
echo "# should show no parents for tip"
hg debugindex .hg/data/bar.i
echo "# should match"
hg debugindex .hg/data/foo.i
hg debugrename bar
echo "# should show no copies"
hg debugstate|grep '^copy'
exit 0