Documentation improvement
Bug in output format for JPG set fixed

The format of the training set can be changed with the `-pngoutput` key.
Output image will be resized to a 640x480 size if greater.

see https://github.com/Itseez/opencv/pull/3137

Conflicts:
	modules/core/src/matmul.cpp

A self-assignment leads to a call of release() with refcount being 2. In the release() method, refcount is decremented and then successfully checked for being 1. As a consequence, the underlying data is released. To prevent this, we test for a self-assignment

fix should be applyed for every window interface and generation