This fixes all problems from the article "Checking OpenCV with PVS-Studio"
<http://www.viva64.com/en/b/0191/> that are not already fixed and are
not in 3rdparty or the legacy module.

The problems fixed are two instances of useless code and one instance
of unspecified behavior (right-shifting a negative number).

call dst.create(...) before using it

fixed slow down in getRectSubPix (original patch by Markus JR Mueller); removed some unused variables and functions

Conflicts:

	modules/core/src/stat.cpp