BUG: ImageAccumulate overflows for large images

If, in a large image, the count for a bin exceeds the max for an
integer, the count overflows and reports the wrong value. This patch
changes the output of ImageAccumulate to an image of vtkIdType.

The patch include a test. To truly validate a configuration, the dimensions
for the test should be set to 2048. For routine testing a small
dimension is recommended.

This bug was uncovered and analyzed by Gib Bogle while trying to use
ImageAccumulate on very large tiff images.

Change-Id: I284bf503e59461acf2c2d1ffb340daa4979582c2
Reduce code duplication for Start() method.

All the interactor subclasses had duplicated code in their Start()
methods, so I moved the common code into the superclass, and made a
new protected method called StartEventLoop() that contains all of
the OS-specific code.

Change-Id: Ib710fad013aa9400d21241cf285c23b4a6cdad9f
Ensure python header version matches lib version.

There was an error in the foreach() loop over _Python_VERSIONS.
Even if the python library for a specific version was not found,
it would try to find the include file for that python version.
As a result, it could very easily find the include file for one
version of python, and the library for another version.  This has
been seen to happen on OS X, but could happen on any OS.

Change-Id: I90157ba517dadd7d1ba0ce1f5dba523246064581
Remove the deprecated PYTHON_INCLUDE_PATH variable.

This variable has been deprecated for years and its presence can
lead to extreme frustration.  If it is set in the cache, then it
is used as the PYTHON_INCLUDE_DIR.  That means that if someone
removes PYTHON_INCLUDE_DIR from their cache (e.g. while trying to
debug their build), then cmake will set PYTHON_INCLUDE_DIR from
the internally cached PYTHON_INCLUDE_PATH instead of searching the
system for Python.h like it should.

Also fix the variable names in the documentation for this macro,
which were different from the names of the variables that were actually
used.

Change-Id: I55d54b9d05085118c97a2e1d417e8e6b31289f8a
Re-added gradient opacity

Change-Id: I3663c0aa6a63cb2848b218df8bf3689972c27c3f
Wrapped long lines

Change-Id: I4bc884eb7e7cf847bdba1539e59e76e5936b9a2e
Organzied the code bit better

Change-Id: Ic2583f8a9f1f96cd5f59fdb749dfa9aabd9c50a6
Disabled the gradient opacity test for now

Need to find a better dataset

Change-Id: I07538bb17bade78e497bca4516acbeea0596a487
Fixed failing tests

Change-Id: Ie746b625312ced6ca333f564e1c116bf97319884
Merge topic 'python-version-match' into master

698f17d6 Remove the deprecated PYTHON_INCLUDE_PATH variable.
8d2ae20d Ensure python header version matches lib version.
Merge topic 'ImageAccumulateBinOverflow' into master

a9527207 BUG: ImageAccumulate overflows for large images
Fix Initialize() and Start() interactor documentation.

Change-Id: I2ab1c29b395d1f24089913ed30905312f9ad8a05
FIX: Exclude the vtkRenderingOpenGLNew module from BUILD_ALL_MODULES

Change-Id: Ieb1372504b1d866893b601823a2b30755d996dc6
Merge topic 'consolidate-interactors' into master

55e5b2ec Fix Initialize() and Start() interactor documentation.
5dbbc8e9 Reduce code duplication for Start() method.
FIX: Use RegressionTestImage instead of InteractorEventLoop

The hypothesis is that InteractorEventLoop was not creating
the OpenGL context in time for glew to find extensions for.

Change-Id: I5b7df0c5b1cbac4e7da8d30d60963a6b1158b122
Merge topic 'volume_rendering_gradient_opacity' into master

59a2a484 Fixed failing tests
ff4d6085 Disabled the gradient opacity test for now
bad034c5 Organzied the code bit better
3b60ff0e Wrapped long lines
85b6fbf8 Re-added gradient opacity
Merge topic 'exclude_new_volume_rendering_module' into master

4f78b2ab FIX: Exclude the vtkRenderingOpenGLNew module from BUILD_ALL_MODULES
FIX: Disable new volume rendering tests for old mapper

Change-Id: Id3b05fe548873ea43f51fa2097550a334e8538c2
FIX: Exclude vtkRenderingVolumeOpenGLNew from vtkOpenGL kit

This fixes the issue that when the vtkOpenGL kit is turned ON,
the vtkRenderingVolumeOpenGLNew module should not be built.

Change-Id: Icca73fa738567a0fd37e0e498d82d4b99d08b253
Merge topic 'new_volumerendering_tests' into master

d2cd5d74 FIX: Disable new volume rendering tests for old mapper
9d74a3ef FIX: Use RegressionTestImage instead of InteractorEventLoop