a new combo box

[Matthias Clasen <matthias clasen gmail com>]

Hi,

over Christmas, I had some for a little side project, a  new combo
box. It is based on these mockups:
https://raw.githubusercontent.com/gnome-design-team/gnome-mockups/master/theming/widgets/combobox-replacements.png

One question I need some feedback on is naming: We currently have
GtkComboBox and
GtkComboBoxText. I've gone with GtkCombo for now, which has the
downside that there is a widget by that name in gtk2. Alternatives
might be GtkChoice or GtkComboButton (with a possible avenue for
making the list-of-choices available for direct embeeding as
GtkComboWidget later).

There are some lose ends in the code, like the interaction of grouping
and search, but it is complete enough to give it a try and evaluate
the design. If you want to try it, the code is in the wip/combo
branch, and there is a testnewcombo test app with some examples.

I'm off for a few days now - would be great to hear some feedback when
I come back.

Matthias