COMP: Update all cmake versions to 2.8.6

As of https://github.com/InsightSoftwareConsortium/ITKExamples/commit/b41daae8847e61d4e2b8aa21b8fe78a7c63ac34a
the minimal cmake version was updated to 2.8.6

This patch updates all the version tags in all the files;
it also removes some old code for cmake 2.8.5 and 2.8.4,
which I already removed from ITK.

Change-Id: Ief844ef5caec9098d04a07a43961af803852662e
Merge "COMP: Update all cmake versions to 2.8.6"