Fixes #4937.  The filteringselect initial setvalue was failing since "" was not a valid value and thus it refused to call setvalue.  Thus the user selected value became the first value and was thus ignored by _formwidget.  This is especially confusing since the filteringselect setvalue is asynchronous, so _formwidget doesn't know how long to wait for the initial setvalue.  To avoid this parallox, I defined the priorityChange boolean of setValue to be null during postCreate, so _formwidget can detect if a setvalue should be ignored or not.
Fixes #4937.  The filteringselect initial setvalue was failing since "" was not a valid value and thus it refused to call setvalue.  Thus the user selected value became the first value and was thus ignored by _formwidget.  This is especially confusing since the filteringselect setvalue is asynchronous, so _formwidget doesn't know how long to wait for the initial setvalue.  To avoid this parallox, I defined the priorityChange boolean of setValue to be null during postCreate, so _formwidget can detect if a setvalue should be ignored or not.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@11247 560b804f-0ae3-0310-86f3-f6aa0a117693

harbalk/delite,kitsonk/delite,Sam-Cummins/delite,harbalk/delite,Sam-Cummins/delite,kitsonk/delite