libpng 1.5+ recommends a call to png_set_interlace_handling() if you use
png_read_update_info and png_read_image. It will generate a warning
without it.

Also removed malformed tEXt chunk from a logo PNG.

See pull request #1241 for why.

do not calculate sum of error in every round of iteration;
instead the error will be summed every 2nd times or more, 
if the previous sum of error is too far away from threshold.

* use explicit extrapolation only for sub-matrixes
* use built-in interpolation for INTER_NEAREST mode

Changed the brief description of function Mat::colRange from "Create a matrix header for the specified row span." to "Create a matrix header for the specified column span."