Document that Iterator(image, region) constructors initialize at the begin, add GTest unit test#4815

dzenanz merged 2 commits intoInsightSoftwareConsortium:masterInsightSoftwareConsortium/ITK:masterfrom

N-Dekker:GTest-ImageRegionIterator-CheckBeginAndEndN-Dekker/ITK:GTest-ImageRegionIterator-CheckBeginAndEndCopy head branch name to clipboard