vtkParticleTracerBase::PreviousOutputPointData needs to shallow copy
OutputPointData instead of pointer-copy. This is fixed. It is also
renamed to something better: ParticlePointData, with comments added.

The "<" operator for StreakParticle needs to return false for
equality. Otherwise, stl sort will crap out with memory corruption.

Fixed a spurious warning

Change-Id: I2e2c6aa1defab135fc6f9b5767ed7f03ba1bcc92