run-tests: fix _checkhglib() so it's correct when using --with-hg.
Since this makes the warning less likely, upgrade it to a "real"
warning to stderr.
#!/bin/sh
"$TESTDIR/hghave" symlink || exit 80
hg init a
cd a
echo '% directory moved and symlinked'
mkdir foo
touch foo/a
hg ci -Ama
mv foo bar
ln -s bar foo
echo '% now addremove should remove old files'
hg addremove