update-copyright: handle more cases * build-aux/update-copyright: Handle cases like gunzip.in with its two copyright lines. Making it work required two changes: don't stop upon first match. And then, when continuing, a little trickiness: knowing that the final substitution would reset m{}g's "pos()", so save and restore that, to avoid an infinite loop in some cases. * tests/test-update-copyright.sh: Add a test for this.