COMP: fixed license test command in UpdateDoubleConversionFromGoogle.sh

The script commands to check that the DoubleConversion license
hasn't changed since the last update from the upstream Google
repository were apparently untested, and did not work.

I replaced them with bash commands that did what was intended.

Change-Id: I36a13daf2cd72e7fc27a0adb15331b652e482349
COMP: Adding itkMacro.h for ITK_NULLPTR definition

Error detected by ITK's header test.

Change-Id: Ia3ff7792b2bf18bf38e36fbc1e89dcba508768aa
Merge topic 'FIX_DOUBLECONVERSION_UPDATESCRIPT'

00e18c24 COMP: fixed license test command in UpdateDoubleConversionFromGoogle.sh
Merge topic 'FixMissingHeaderForITK_NULLPTR'

e2927dab COMP: Adding itkMacro.h for ITK_NULLPTR definition