Add multi-block support to the "Temporal particles to pathlines" filter
When using a data-set with multiple spatial blocks, where the temporal information is present in the top-level multi-block wrapper node,
the pathlines filter does not find any timestepping information.
(cf. related discussion on the mailing list: http://www.paraview.org/pipermail/paraview/2010-October/019042.html)
Since we produce our data massively in parallel, we can not write a single spatial block efficiently and must rely on xdmf's multi-block capability. Without an efficient trajectory-trace filter, however, particle plotting using paraview is obviously mostly pointless.