VTKRecorder exports misleading i.phys.isOnJoint in periodic conditions

Imagine a joint surface with Lz (z-dimension of this surface) lower than z-extents of the sphere sample. In periodic conditions, Paraview displays also as "isOnJoint" the interactions that are "above" the considered joint surface. Contrary to what really occurs in the yade model.

In non-periodic conditions, the problem disappears : infos of VTKRecorder displayed through Paraview are consistent with the ones obtained directly through Yade command line.

An example script will maybe be given soon... (personal note : see e.g. tecPC1)

Original bug report by Jérôme Duriez on 2014-05-19 : https://bugs.launchpad.net/yade/+bug/1320852