ENH: Build against ITKv4 and VTK6.

Change-Id: Iac752abb6843d3399841c152f6486c8297d479bd
COMP: Only use -ffast-math with g++.

Clang currently has a bug that results in a build error:

  In file included from ../../../progs/TubeTK/Applications/RegisterUsingImageCenters/RegisterUsingImageCenters.cxx:26:
  In file included from ../../../progs/TubeTK/Utilities/tubeCLIFilterWatcher.h:26:
  In file included from ../../../progs/ITKStable/Modules/Core/Common/include/itkSimpleFilterWatcher.h:23:
  In file included from ../../../progs/ITKStable/Modules/Core/Common/include/itkTimeProbe.h:22:
  In file included from ../../../progs/ITKStable/Modules/Core/Common/include/itkResourceProbe.h:100:
  In file included from ../../../progs/ITKStable/Modules/Core/Common/include/itkResourceProbe.hxx:32:
  In file included from ../../../progs/ITKStable/Modules/Core/Common/include/itkNumericTraits.h:46:
  In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include/g++-v4/complex:45:
  In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/4.6.3/include/g++-v4/cmath:45:
  In file included from /usr/include/math.h:424:
  /usr/include/bits/math-finite.h:177:1: error: unknown type name '__extern_always_inline'
  __extern_always_inline double __NTH (lgamma (double __d))
  ^
  /usr/include/bits/math-finite.h:177:24: error: expected unqualified-id
  __extern_always_inline double __NTH (lgamma (double __d))
                         ^
                         /usr/include/bits/math-finite.h:186:1: error: unknown type name '__extern_always_inline'
                         __extern_always_inline float __NTH (lgammaf (float __d))
                         ^
                         /usr/include/bits/math-finite.h:186:24: error: expected unqualified-id
                         __extern_always_inline float __NTH (lgammaf (float __d))
                                                ^
                                                /usr/include/bits/math-finite.h:196:1: error: unknown type name '__extern_always_inline'
                                                __extern_always_inline long double __NTH (lgammal (long double __d))

Change-Id: I872d776969c7694d8b0d5bc660fc5367825e99ed
ENH: Use ITKv4 by default.

Remove ITKv3 from the superbuild.

Set Insight superbuild tag to v4.3.1 so the project is consistent
when performing a checkout and so the it does not keep rebuilding.

Change-Id: I4167a4f1aade83547495ecd98233b025723eddcb
ENH: Clean up ITK_VERSION_MAJOR macros.

Clean up ITK_VERSION_MAJOR preprocessor macros
with the switch to ITK4.

Change-Id: Icb39abf9f64164eb1c59c578955052f584852cf7
COMP: Fix remaining ITKv4 related test failures.

Issues:

- Virtual function signatures.
- Differences in baselines corrected due to a correction in how spacing/sigma
is calculated in ITK RecursiveGaussian filters (ITK b54b8f664c).
- Fix bugs introduced in previous ITKv4 transition patches.
- Fix style issues noticed when reading through the code.
- One input needed to be a MHA instead a PNG like the MHA it was being compared
to since ITKv4 is more strict about origin/spacing alignment (and PNG does not
store these).

Change-Id: I7fea46c9b81aa52d13f9569d5b4c3bbded2875fd
ENH: Integrating Slicer4 into the build.

Also, with these changes it should build with GCC 4.7.1.

Change-Id: I6606a511b5a2603734927eaa8bdea207c2a3e649
BUG: Fix path to PrintSelfCheck.py.

Change-Id: I2c486f8b62d6928d541170f2e2f0ef7a118a3a53
Merge topic 'ITKv4VTK6_4'

48c0db7 BUG: Fix path to PrintSelfCheck.py.
607b4dc ENH: Integrating Slicer4 into the build.
1ff75fd COMP: Fix remaining ITKv4 related test failures.
1ece57e ENH: Clean up ITK_VERSION_MAJOR macros.
c24ebdf ENH: Use ITKv4 by default.
f847503 COMP: Only use -ffast-math with g++.
c53d9c5 ENH: Build against ITKv4 and VTK6.