BUG: Use rounding in TestingStretchIntensity for portability

Change-Id: I803869ba6524e4e25bfdee9bed196df20769078d
BUG: Warn if unsupported ITK_BRAINWEB_DATA_ROOT is being used

Several system on the dashboard are still using this flag. Emit a
CMake warning so that these build can be identified an updated.

Change-Id: Ie64bc39680b850a9ca2596c5a864267fcfaedb39
Merge topic 'UseRoundInTestingStretch'

bcc998ae BUG: Use rounding in TestingStretchIntensity for portability
Merge topic 'WarnAboutOldBRAINWEBCMakeVariable'

00e44d53 BUG: Warn if unsupported ITK_BRAINWEB_DATA_ROOT is being used