Fix: freeing previous elements has to be done before loading new parameters to avoid trying to delete unexisting objects if arrays size was modified

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.

Original author: me.

Original author: Alex Wilson.

This reverts commit a9975b14, to prepare
for cherry-picking upstream's solution.

We don't use -Wcast-align ourselves, but the headers trigger warnings
for those users who do, which is not nice.

This is fixed upstream in mariusmuja/flann@b615f26, but that fix
would break binary compatibility, so I had to make a different one.

Since the bug isn't quite obvious, here's an explanation. In the const
version of any::cast, if policy is a small_any_policy, its get_value
returns its input argument. So r becomes a pointer to obj, and the
return value is a reference to a local variable, which is invalidated
when the function exits.

Looks like we don't actually use them; when creating precompiled headers
with Visual C++, a dummy .cpp is created at build time.

Fixed flann build with NEON;
Fixed Haming distance with NEON;
Honest cvRound for WinRT added;
cvRound test added;
Video IO with direct show disabled;

All tests passed!

e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

Made all STL usages explicit to be able automatically find all usages of
particular class or function.

Invalid links and refences fixed.
SpaeseMat class documentation updated.