BUG: Fix GDCM buffer size when written pixel type is different.

Previous value was twice its correct value in itkGDCMSeriesReadImageWriterTest
where the written pixel type is short and the pre-rescaled pixel type is char.

Change-Id: I16537fac89c5937f9c7ec2017c091fba8a896b56
BUG: Set output type to unsigned char when writing uchar in GDCMIO test.

In itkGDCMSeriesReadImageWriteTest, the GDCMImageIO is re-used on a writer
that is writing a unsigned char image.  However the ImageIO was originally
used to read an unsigned short image, and writing unsigned char data to an
unsigned short DICOM file is not supported by DICOM.

Use SetInternalComponentType to set the correct internal component type when
writing the unsigned char file.

Change-Id: I5410afc22678990a173e3bcfe578cfc984e16763
Merge topic 'GDCMRescalePixelTypes2'

1edae060 BUG: Set output type to unsigned char when writing uchar in GDCMIO test.
ce503c43 BUG: Fix GDCM buffer size when written pixel type is different.