Set MultipleSelect initial value after setting it to be multiple select
Set MultipleSelect initial value after setting it to be multiple select

Only one value is selected otherwise.

Fixes #106

SylvainCorlay/ipywidgets,cornhundred/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,cornhundred/ipywidgets,jupyter-widgets/ipywidgets,cornhundred/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets