Assume UTF8 for vtkCarbonRenderWindow::SetWindowName

Since VTK now uses UTF8 in other places, use it here too instead
of ASCII.  This is backwards compatible.

Change-Id: I32dc7174e1460f27c8e73e6fb6b8982f2d35d0b7
Merge topic 'carbon-utf8' into master

5a568d2c Assume UTF8 for vtkCarbonRenderWindow::SetWindowName