BUG: GDCM Series does not write z-spacing.

When a GDCMImageIO is used with an ImageSeriesWriter, the z-spacing is not
written to the output image.  The ITK_Spacing metadata passed was not being
added to the output.  m_NumberOfDimensions is only 2 in this case.  If there
is a z-spacing that is set, it should be passed.

Change-Id: Ia8744c7d391e2e80e06b7843224f44a5398a55e5
Merge branch 'master' into gdcm-spacing-release2

Conflicts:
	Modules/IO/GDCM/test/CMakeLists.txt

Change-Id: I5182d1848faa9dc0b8bc48bab1556bb26af1e4dd
Merge topic 'gdcm-spacing-release2'

55b14edb Merge branch 'master' into gdcm-spacing-release2
f878fa7c BUG: GDCM Series does not write z-spacing.