Updating STAR detector and FREAK descriptor to work with large and/or 16-bit images
Don't automatically convert to grayscale (keep previous behavior.)
Merge branch 'master' of https://github.com/Itseez/opencv

Conflicts:
	modules/imgproc/src/sumpixels.cpp
When a cluster is empty for KMeans, it's better to give it the point from another cluster j that is the furthest one from center j.
Add a new method for initializing KMeans centers that leads to better clusters and thus better retrieval when final centers have to be existing keypoints instead of clusters barycenters.
converted necessary files for python3 compatibility using 2to3
fixed relative imports in Jinja for python3
explicit string encoding when writing to file in python3
added epsilon value to weights in the MergeMertens in order to avoid zero weights for pixels from uniformly filled areas of image
added test for correct handling of uniforma areas in the MergeMertens
Updated cloud io functionality - removed dependency from VTK legacy
More proper OpneCv+Qt+Vtk issues handling (http://code.opencv.org/issues/3492)
cloud collection merges data only on rendering
fixed size_t/int conversion warnings
proper render call order (fixes some issues with VTK6.1)
default meshlab background
Fixed all OpenGL issues for Macos (via objective-C++ layer)
cloud collection finalize
casting Vec3b operator for viz::Color
Added WidgetMerger, Polyline - colors support for each point independently, simple widgets now compute color array instead of setting global color