Combobox improvements

[tstanley]

I like the Combo Box controls which are available in CVI, and I think there is some room for some improvements.

1.  Make their appearance more similar to the available Ring controls.  Right now the Combo Box has a look unlike the other available controls which can make a UIR that mixes Combo Boxes with Rings and Lists rather jarring.

2.  A numeric Combo Box control.

Thanks.

[tstanley]

Just found out that the source is available in combobox.c.  Will have to poke around.