Fixed inconsistency with flag names for solvePnP. 
The default value for the function lacks the CV_ prefix. The code checks against "ITERATIVE". The suggested values for the parameters *include* the prefix.
Even though the enum CV_ITERATIVE (+ CV_P3P, CV_EPNP) = ITERATIVE (& P3P, EPNP), lets show to the users only one of them.
Now the user sees only {ITERATIVE, P3P, EPNP}.

The keys() and values() functions on dictionaries in Python 3 no longer
return lists.  pyopencv_to() for flann::IndexParams now iterates over
the dictionary in a way that is version-agnostic.

Conflicts:
	doc/tutorials/introduction/linux_install/linux_install.rst
	modules/core/doc/operations_on_arrays.rst
	modules/core/include/opencv2/core/core.hpp
	modules/core/src/system.cpp
	modules/gpu/src/cuda/resize.cu
	modules/imgproc/doc/miscellaneous_transformations.rst
	modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst
	modules/video/src/bgfg_gaussmix2.cpp