Author: Stephan Kramer
Revision Date: 2014-02-19 10:50:17 UTC

Speed up of vtudiff for vtus with multiple fields.

This is done by only setting up the VTK probe once instead of once per field. It does not change anything in the way fields are probed.
This commit also enables the diffing of cell-based (P0) fields in the vtu (only works if they are on the same mesh).

There is also a little bit of cleaning up in vtktools:
* removing the option to call vtktools as a main: this really doesn't make sense and should be in a separate script
* removing the "field manipulation" methods. These were basically vectorial operations on fields but implemented in a rather inefficient way. I see no reason to not simply use numpy vector operations for that, so instead of:

vtu.SubFieldFromField("fieldName", array, "newFieldName")

just do:

field = vtu.GetField("fieldName")
vtu.AddField("newFieldName", field-array)