Patched the issue of Niftyreg's pngtest overriding the main() function of...

Patched the issue of Niftyreg's pngtest overriding the main() function of SuperElastix client applications (including SuperElastix Google tests). Still hoping that Marc Modat will fix this issue at https://cmiclab.cs.ucl.ac.uk/mmodat/niftyreg

SuperBuild/ExternalNiftyreg.cmake

@@ -26,6 +26,7 @@ ExternalProject_Add( ${proj}
   GIT_REPOSITORY ${NIFTYREG_GIT_REPOSITORY}
   GIT_TAG ${NIFTYREG_GIT_TAG}
   UPDATE_COMMAND ""
+  PATCH_COMMAND "${GIT_EXECUTABLE}" reset --hard && "${GIT_EXECUTABLE}" apply --whitespace=fix "${CMAKE_SOURCE_DIR}/Patches/Niftyreg_remove_pngtest.patch"
   SOURCE_DIR ${proj}
   BINARY_DIR ${proj}-build
   CMAKE_GENERATOR ${gen}

SuperBuild/Patches/Niftyreg_remove_pngtest.patch

+--- a/reg-io/png/CMakeLists.txt
++++ b/reg-io/png/CMakeLists.txt
+@@ -45,7 +45,6 @@ if(BUILD_INTERNAL_PNG OR BUILD_ALL_DEP)
+ 				lpng1510/pngrtran.c
+ 				lpng1510/pngrutil.c
+ 				lpng1510/pngset.c
+-				lpng1510/pngtest.c
+ 				lpng1510/pngtrans.c
+ 				lpng1510/pngwio.c
+ 				lpng1510/pngwrite.c

SuperBuild/Patches/Niftyreg_remove_pngtest_ReadMe.txt

+We found that pngtest.c should be excluded from libpng when linked to Niftyreg, because its main() function sometimes overrules the main() of a SuperElastix client application.
+
+As Floris mailed to Marc, the creator of Niftyreg:
+
+  From: Berendsen, F. (LKEB)
+  Sent: Friday, April 21, 2017 4:58 PM
+  To: 'm.modat (at) ucl.ac.uk'
+  Cc: Dekker, C.E. (LKEB)
+  Subject: Solving issue with pnglib
+