make vtkTreeHeatmapItem tolerate missing input

Avoid segmentation faults when SetTree or SetTable are called with
NULL arguments.  Update GetBounds so that it no longer assumes both
a tree and a table have been loaded.

Change-Id: I72ad76a996136aeeaf0c06d25ebe70078d1075c5
Merge topic 'fix_heatmap_crash' into master

76d6ab2e make vtkTreeHeatmapItem tolerate missing input
Don't create an object library for Python wrapping

It requires CMake >= 2.8.8 and avoids duplication of ~5 lines of code
anyways, so it isn't needed.

Change-Id: Idbc6bf192a31692788cf7c259cd749b32f85a778
COMP: Populate vtklibproj4 link interface

This was missed in the cleanup-CMP0022-CMP0023 branch.

Change-Id: Icb4625345e24561f21b540a9e86c2c02ab0b54c9
Merge topic 'unified-bindings-no-object-library' into master

179c7551 Don't create an object library for Python wrapping
Merge topic 'vtkproj4-linking' into master

c549f584 COMP: Populate vtklibproj4 link interface