Gio::Menu: Allow detailed_action == null

* gio/src/menu.hg: insert/prepend/append(): Make it possible to pass
detailed_action == 0 to the glib/gio functions. Bug #733203.
2.41.2
doap category core
doap: add <programming-language>
Network example: Add --use-ipv6 command line option

* examples/network/socket-client.cc:
* examples/network/socket-server.cc: Add --use-ipv6 command line option.
Bug #734094.
Network example: Use Glib::OptionEntry and friends

* examples/network/socket-client.cc:
* examples/network/socket-server.cc: Use Glib::OptionEntry, OptionGroup,
OptionContext instead of the glib equivalents.
Merge branch 'master' of git://git.gnome.org/glibmm
JOHNE - Bump the version number to 2.41.02