DOC: Fix description of SpatialObject::GetBoundingBox()

Change-Id: I0bbc0e3a9711651b1e0ef98544c44d94b2726f65
COMP: Use latex formula for HoughTransform doxygen.

The std:: prefix causes a warning:

  Generating docs for compound
  itk:/.../ITK/Modules/Filtering/ImageFeature/include/itkHoughTransform2DLinesImageFilter.h:34:
  warning: explicit link request to 'cos(Teta)' could not be resolved

Use a better LaTeX formula.

Change-Id: I39c6e98dabcbd5e4606a755114f67084ca942ecf
COMP: SigmoidTransferFunction members Alpha, Beta real type.

For:

  /scratch/dashboards/Linux-x86_64-gcc4.1/ITK/Modules/Numerics/NeuralNetworks/include/itkSigmoidTransferFunction.hxx:33:
  warning: converting to 'unsigned char' from 'double'

Change-Id: I8c965d785d7bac8474ff24c402a36efb1d103274
STYLE: Fix SigmoidTransformFunction template argument names.

Change-Id: I418d256612a86a65b6e3aaa86e92e470d4ba72ab
ENH: Replace python print with print() function

This is needed for python 3 and is backward compatible with python 2.7 and 2.6.

Some prints were commented out, I just added the parantheses, to be consistent throughout the code.

I did not update:
- gdcm Python files (third party)
- notyetusable Python tests, those need refactoring anyway
- the Python examples, they are being moved to the itk examples repo

Change-Id: If527aacb1c379165c2188dfa8f85c28ed55ed4c9
Merge topic 'Python3Print'

621872a2 ENH: Replace python print with print() function
COMP: BuildHeaderTest.py print_function import.

Needs to be at the top of the file.

Change-Id: I33d23d9482c2c91f00cc2c284f952e7f99f49883
Merge topic 'headertest-print'

df2af6d6 COMP: BuildHeaderTest.py print_function import.
Merge topic 'houghlines-formula'

1e724e93 COMP: Use latex formula for HoughTransform doxygen.
Merge topic 'SpatialObjectDoc'

5bb373de DOC: Fix description of SpatialObject::GetBoundingBox()
Merge topic 'sigmoid-warning'

e5124114 STYLE: Fix SigmoidTransformFunction template argument names.
b69e7653 COMP: SigmoidTransferFunction members Alpha, Beta real type.
COMP: Fix failing header test

Disable this test if Python version is less than 2.6.

The fixed error:
  File "/scratch/dashboards/Linux-x86_64-gcc4.1/ITK/Utilities/Maintenance/BuildHeaderTest.py", line 21
    from __future__ import print_function
SyntaxError: future feature print_function is not defined

Change-Id: I14c525e3aff46b78edcf9d2690d8bf0bb2b29061
Merge topic 'HeadertestPython2.6'

0ff8be3d COMP: Fix failing header test
PERF: Minimize redundant function calls

The highest percentage of time in the MattesMutualInformation
filter was spent evaluating if specialized work needed to
be done for displacment fields.

In a minimalistic test case, prior to this change the registration
took 846 seconds, after this change, registration tok 309 seconds.

bin/BRAINSFit   \
  "--costMetric" "MMI"  \
  "--failureExitCode" "-1"   \
  "--numberOfIterations" "1"  \
  "--numberOfHistogramBins" "50"  \
  "--splineGridSize" "7,5,6"  \
  "--numberOfSamples" "14000"   \
  "--minimumStepLength" "0.1"  \
  "--initializeTransformMode" "useCenterOfHeadAlign"  \
  "--transformType" "BSpline"  \
  "--fixedVolume" "/scratch/johnsonhj/src/NEP_ICC-getp/BRAINSTools-build/ExternalData/TestData/test.nii.gz"  \
  "--movingVolume" "/scratch/johnsonhj/src/NEP_ICC-getp/BRAINSTools-build/ExternalData/TestData/rotation.rescale.rigid.nii.gz"  \
  "--outputVolume" "/scratch/johnsonhj/src/NEP_ICC-getp/BRAINSTools-build/BRAINSFit/TestSuite/BRAINSFitTest_BSplineScaleRotationRescaleHeadMasks.test.nii.gz"  \
  "--outputTransform" "/scratch/johnsonhj/src/NEP_ICC-getp/BRAINSTools-build/BRAINSFit/TestSuite/BRAINSFitTest_BSplineScaleRotationRescaleHeadMasks.h5"  \
  "--maxBSplineDisplacement" "7.3"

Change-Id: I3782e78cae99acfe577a40444882688ae5b76472
PERF: Pull loop termination constants out of loop

When evaluating loops, loop termination criteria that
are accessed via member functions should not be
used at every iteration.  Common static loop iteration
termination values are stored locally and reused.

Change-Id: Ia847f411640cce6921b28ac2a2da448c40ebe24c
WIP: Another set of minor loop performance improvments.

Change-Id: Ibf63ca97d07cd5ab95af81ced19936f13d728799
WIP: More loop indicies end optimiations.

Change-Id: I83e6c9ca05066b29e5a57ecf520dcf6e9b95d62b