Filter was modifying self in request. Fixed.

Filters are not allowed to call functions that call their MTime
to update during any request passes. vtkParticleTracerBase was
calling a Set method that did that. Fixed.

Change-Id: I2381c8400eff3d6a081df796ca5726fc89d75a96
Merge topic 'filter-modified-in-request' into master

dca4464c Filter was modifying self in request. Fixed.