set reslicesd image member to null in early out
Checks now if there is a mask in use, or if method is only called by the use of
"Ignore zero-valued voxels".
Merge branch 'bug-13582-HistogramBarchartErroneousByIgnoreZeroValuedVoxels'
USE_OpenCL variable now passed from superbuild to MITK-build
Merge branch 'bug-13813-OpenCL-BuildSystem'
Fixed and reactivated failing downsampling filter test.
Merge branch 'bug-12100-BugFixes'
enhanced documentation for SetSourcePath
Merge branch 'bug-13821-oclsourceloadpath'
Added more documentation why we set this member to null.
Merge branch 'bug-13275-different-geometryreslice'