BUG: Reduce tolerance for same slice checks

The AlmostEquals function fails for slices that are only 1e-15 different
for 1.5mm slices.

The DefaultImageCoordinateTolerance has been determined to be 1e-6.

Using the global default tolerance provides more meaningful default
behaviors.

Modules/IO/ImageBase/include/itkImageSeriesReader.hxx

@@ -27,6 +27,7 @@
 #include "itkMetaDataObject.h"
 #include <cstddef> // For ptrdiff_t.
 #include <iomanip>
+#include "itkImageBase.h"
 
 namespace itk
 {
@@ -432,9 +433,8 @@ ImageSeriesReader<TOutputImage>::GenerateData()
         SpacingScalarType dirNnorm = dirN.GetNorm();
 
         if (this->m_SpacingDefined &&
-            !Math::AlmostEquals(
-              dirNnorm,
-              outputSpacing[this->m_NumberOfDimensionsInImage])) // either non-uniform sampling or missing slice
+            std::abs(dirNnorm - outputSpacing[this->m_NumberOfDimensionsInImage]) >
+              itk::DefaultImageCoordinateTolerance) // either non-uniform sampling or missing slice
         {
           nonUniformSampling = true;
           spacingDeviation = itk::Math::abs(outputSpacing[this->m_NumberOfDimensionsInImage] - dirNnorm);