ENH: Use partial template specialization for iso value vis

Change-Id: Idf13cdf9ac1c2ccc136d3b2a306c8309930cb68c
PERF: Allow delete of NULL pointers

The deletion of a NULL value is a no-op in C++. Simplify code
by removing superfluous checks for NULL before deletions.

Part of issue: https://issues.itk.org/jira/browse/ITK-3182

Change-Id: I170fa7e143184fa5952e093e2884a3de7c527d71
ENH: Use file(COPY .. instead of exec_process.

exec_process is deprecated, and it is more efficient to avoid spawning a
process.

Change-Id: I72545d2acdd3f70f2814e49382593bc13f9e7d8f
BUG: Fix memory leak error in itkHDF5TransformIO

There was a Valgrind error in itkIOTransformHDF5Test after the
TransformIO new API patch is merged.
The memory assigned to the double precision buffer was not freed after
it was used.
This error is addressed in this patch.

Change-Id: Idf6801cd8187cd244c2cdc36978dbdd570cae138
Merge topic 'valgrindMemoryLeak'

105887f BUG: Fix memory leak error in itkHDF5TransformIO
Merge topic 'Delete-Null'

a28028d PERF: Allow delete of NULL pointers
Merge topic 'WrapITKErrors'

e37610c ENH: Use file(COPY .. instead of exec_process.
Merge topic 'FixVisuLevelSet3D'

12b38cf ENH: Use partial template specialization for iso value vis