Copyright-holder and year information is extracted from git log.
git history begins in 2005. So (C) from 1998..2005 is lost. Also some
(C) assignment of commits where the committer didn't use --author.
Since 5.8-245-g3e43585fa, a response hides the dialog Window
in ArdourDialog::on_response (to prevent dialogs windows staying
around unresponsively while Ardour does background work).
This logic does not apply to Dialog Windows which implement
ProgressReporter or support dialog responses other than OK, Close.
