Fixed getSubset method to support Nx3 1-channel matrices as input (3xN 1-channel matrices doesn't supported at all).

Changed parameter order in documentation of findEssentialMat, because threshold and probability were switched.

Extension of the camera distortion model for tilted image sensors (Scheimpflug condition) including test

so it matches the code.

the first order approximation of the geometric error

Make a note about 16-bit signed format - the function assumes that
values have no fractional bits (so 16-bit disparity from StereoBM
and StereoSGBM cannot be directly used!)

Fixed small mistake in documentation.
The prism coefficients in y'' equation were mistakenly written as s1,s2 instead of s3,s4

New mode is approximately 2-3 times faster than MODE_SGBM
with minimal degradation in quality and uses universal
HAL intrinsics. A performance test was added. The accuracy
test was updated to support the new mode.

It took me a while to figure out what was meant with

    OpenCV Error: Assertion failed (i < 0) in getMat

While searching for this error message I found [a list of error
messages](https://adventuresandwhathaveyou.wordpress.com/2014/03/14/opencv-error-messages-suck/)
which also explained what the problem was: The data type for `rvecs` was
not a simple `cv::Mat` but a `std::vector<cv::Mat>`.

After I fixed that, I got the next error message:

    OpenCV Error: Assertion failed (ni > 0 && ni == ni1) in
    collectCalibrationData, file
    /build/buildd/opencv-2.4.9+dfsg/modules/calib3d/src/calibration.cpp,
    line 3193

The problem here was that my data type for the `objectPoints` was just
`vector<Vec3f>` and not `vector<vector<Vec3f>>`.

In order to save other people the time looking for this, I added
explicit examples of the needed data types into the documentation of the
function. I had to re-read the current version a couple of times until I
can read the needed levels of `vector<>`. Having this example would have
really helped me there.

Added a mention within calib3d.hpp that the flag RHO is available as an
option on calls to findHomography().

This reverts commit fba72cb6, reversing
changes made to 02131ffb.