Add environment variables for alternate formats and viewers

Added support for the following environement variables:
  SITK_SHOW_EXTENSION
  SITK_SHOW_COMMAND
  SITK_SHOW_COLOR_COMMAND
  SITK_SHOW_3D_COMMAND

SITK_SHOW_EXTENSION changes the file format used from the default Nifti.  It
must be a format supported by ITK.

SITK_SHOW_EXTENSION changes the application used to view images from ImageJ.

SITK_SHOW_COLOR_EXTENSION changes the application used to view color images.

SITK_SHOW_COLOR_EXTENSION changes the application used to view 3D images.

Change-Id: Idc5178758a2ffc4dcf6f57637ecbab76e4c5b0ff
Updated documentation for sitkShow environment variables.

I've augmented the Doxygen documentation for the sitkShow class to describe
the tokens allowed in the SITK_SHOW_COMMAND, SITK_SHOW_COLOR_COMMAND and
SITK_SHOW_3D_COMMAND environment variables.

Change-Id: Ice13ae953e04c14aadc70c23422cf22e26e6820d
ENH: adding support to GetBuffer for vector images

The Image::GetBuferAs... methods now also work with vector images.

Additionally, the PimpleImage class's implementation was modified to
that a cast was not longer needed.
ENH: Added test for GetBuffer of vector images

Performed aditional clean up on the tests of the direction image
attribute.
ENH: adding support for dispatch to functions with 4 arguments
ENH: add new constructor to Image which takes vector and numcomponets

Previously there was not constructor where you could specify the
number of components for a vector image. There would be ambiguilty if
it was just added as another scalar parameters. So a new method was
added where the size is a vector and the last parameter is an optional
number of components.
Fix to include process.h on Windows.

I forgot a header on the Windows build to find _getpid().

Change-Id: I15dca3e798590402dcf3a4b8ae0a21b9a9350d45
Added documentation to Image Constructor.

Restored behavior that vector images default to the number of
components as the ImageDimension. Also a couple bug fixes from rebase
and not initialized the image pimpl pointer.
Adding tests for constructors of vector images.
Fix extraneous common in distutil setup

This appears to be resonsible for the long standing warning:
 Wrapping/PythonPackage/setup.py.in
Fix using uninitialized values in itk::Index

itk::Index must be initialized before use. This addresses long
standing valgrind errors.
Changed var type to match std::string::length.

Went from unsigned int to size_t to fix a Visual Studio 10 compiler warning.

Put #ifndef NDEBUG around debugging print.

I must appease the code gods for my sins.  I left a debugging message
on.

Change-Id: I3ebc9950314d90648c61bd8e072bed9e432133d1
ENH: Use find_package(SimpleITK) in Examples
ENH: moved ITKIntegration into sub directory in example

Created a subdirectory in the Examples which depends on having ITK to
build.
BUG: The BasicFilter libraries were not being added to cmake configs

After the list of libraries became dynamically generated, it was not
correct in the Cmake configure file for other to use the project. The
time when the config file was configure was before the cmake variable
was set in the sub-directories. It is now done at the end of the cmake
file and is correct.
Added Examples as an external project to test SimpleITK installation

Added a new Super build project, SimpleITKExamples which is the
Examples directory as an independent project. This allows for
automatic testing of the SimpleITK installtion. At least the
compilation.
Merge topic 'SIMPLEITK-103_AddedEnvironmentVariables'

102f1c1 Changed var type to match std::string::length.
5c98d0c Fix to include process.h on Windows.
e37cae1 Updated documentation for sitkShow environment variables.
fde84a9 Add environment variables for alternate formats and viewers
Merge topic 'SIMPLEITK-282_AddSupportToGetBufferForVectors'

289d42a ENH: Added test for GetBuffer of vector images
6115818 ENH: adding support to GetBuffer for vector images
Merge topic 'SIMPLEITK-267_ExamplesAsStandaloneProject'

2de209b Added Examples as an external project to test SimpleITK installation
4a6b6b2 BUG: The BasicFilter libraries were not being added to cmake configs
f396582 ENH: moved ITKIntegration into sub directory in example
90fa05f ENH: Use find_package(SimpleITK) in Examples
Merge topic 'SIMPLEITK-283_AddImageConstructorForVector'

6148d8f Adding tests for constructors of vector images.
adf79c2 Added documentation to Image Constructor.
f74d03b ENH: add new constructor to Image which takes vector and numcomponets
fc7abfe ENH: adding support for dispatch to functions with 4 arguments