convert: clear the dirstate before a conversion, invalidate it afterwards
Clearing it before the conversion protects us from whatever data were
there (file copies in particular).
Invalidating it after the conversion avoids writing a possibly
inconsistent dirstate to disk.
#!/bin/sh
"$TESTDIR/hghave" symlink || exit 80
hg init a
ln -s a link
cd a
echo foo > foo
hg status
hg status ../link