Issue #25: DataGrid.hideEditor should not call Focus.

When it is used in Actipro docsite, when the layout is updated due to
the DataGrid lose focus, DataGrid.OnApplyTemplate will be called and
this method will be eventually called. It cause this control to be
activated again.
Merge pull request #26 from raylu1/master

Issue #25: DataGrid.hideEditor should not call Focus.