Since this is usually not the case, showing this all the time as before was so
confusing everyone thought it was broken (myself included).
Changing that show_all() to a show() might have consequences, but it seems to
work fine and we really shouldn't be using show_all() anyway.
git-svn-id: svn://localhost/ardour2/branches/3.0@13889 d708f5d6-7413-0410-9779-e7cbd77b26cf