Merge topic 'pio-reader-variables' into paraview/release

4f4ec425 changes to get rid of compiler warnings
d5c9b9c7 elimate need to specify variables for pio reader

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: David E. DeMarle <dave.demarle@kitware.com>
Merge-request: !6370