Fixes porttable's combobox
Fixes porttable's combobox

Moves the logic in a CompletingComboBox class and adds an explicit
validate_input() call in setModelData().

VisTrails/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,Nikea/VisTrails,minesense/VisTrails,minesense/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,Nikea/VisTrails,hjanime/VisTrails,Nikea/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails,celiafish/VisTrails,celiafish/VisTrails,VisTrails/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails