Change per tree BSF indexing by global BSF indexing.

This global breadth-first search let the user access to point
data in the same order as in the descriptor which describes
the tree representation in BFS.
Moreover, each tree node (even non-leaf ones) can now have
data attached. As previously, the dual only address the tree
leaves.
Updating source, filters and tests to take advantage of this
new behaviour.

Change-Id: I4998336e38cc2d5cf79ec50e51ecc877cb74077e
Fix compilation warnings in vtkpiston.

Change-Id: I5e23b0fe65a91d9e3c54107d9a3a9629cdff096b
Change the indexing of HyperTree and remove dead code & vars.

HT are now indexed in such a way that there is no more
dead index.
HTGSource in quadric mode use the GlobalIndexStart mode to
avoid the storage of the local to global node id per tree
(contrary to descriptor/mask sources which use a BSF global
indexing mode, quadric nodes are numberered on a per-tree
basis).

Also remove some no more used functions and vars.

Change-Id: Ie5fe5f267a22706334d883d330b8aa9bbb3926e2
Clamp integer scalars in InterpolateTuple().

The InterpolateTuple() function was seeing an integer overflow
when used from vtkButterflySubdivisionFilter, and probably had
undetected overflow issues elsewhere.  Adding a clamp to the
interpolation code for integer types protects against overflow.

Change-Id: Ibd6ab7f79d514dbb9ea2d055cc299273b7490f7b
Added polygon selection to hardware selector.

A new Interaction style is added, and the hardware selector is
modifed to handle polygon selection. This new type of selection,
like the rubber band selection, is also based on pixel buffer.

Change-Id: Ic886670fb8cf1bb4a6471b239d8767c03cfea2dc
Merge topic 'polygon_select' into master

962324b7 Added polygon selection to hardware selector.
Merge topic 'Enh-HTG-Add-BSF-GlobalIndexingMode' into master

a45a52a1 Change the indexing of HyperTree and remove dead code & vars.
c5873cf4 Change per tree BSF indexing by global BSF indexing.
Fix warning on HTG 2D FullMaterial test.

Change-Id: Ia3f85f0d0ccf18993dbbdd63ede5ec4fa963da79
Merge topic 'HTG-FixTestWarning' into master

c903fe94 Fix warning on HTG 2D FullMaterial test.
Fix signed/unsigned warning in HTG.

Change-Id: I25be3f3329ab9a228865c64caaf7dfea287fd049
Merge topic 'Fix-HTG-signed-warning' into master

39b7a345 Fix signed/unsigned warning in HTG.
Merge topic 'fix_piston_compwarns' into master

aa810fb8 Fix compilation warnings in vtkpiston.
Merge topic 'clamp-interpolated-scalars' into master

8c73f97f Clamp integer scalars in InterpolateTuple().
Fixing warnings in vtkHardwareSelector

Change-Id: I609f6ea196facc66b91e121f13a1b604521e5d37
Merge topic 'hardwareselector_warnings' into master

030f2931 Fixing warnings in vtkHardwareSelector