When clicked, the option --simplify-by-decoration is added to gitk/git log.
This yields to a simplified history where only decorated commits are shown,
i.e. those with a yellow tag or a green branch flag.
Signed-off-by: Dirk Suesserott <newsletter@dirk.my1.cc> Signed-off-by: Paul Mackerras <paulus@samba.org>