VCS: Make editorparameterwidget comboboxes work with indexes

Change-Id: Id3d81e59f85d9b7d2dbadef337b97be13a37a598
Reviewed-on: http://codereview.qt-project.org/6160


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>