Fix for VTK6.2 issue.
fix python tests
fix bug with invalid signature size (should not be less than signatureLength())
test.py: Check if camera_calibration.tar.gz file exists before downloading it, opencv bug #3782
Merge pull request #2914 from alalek:fix2.4
Merge pull request #2917 from mmaraya:bug_3872
Merge pull request #2905 from Jazmann:2.4