Merge branch 'master' into better_png_transparency

* master: (468 commits)
  added suppression for TBB valgrind issue
  update CUDA architecture flags initialization
  increase minimal supported CUDA toolkit to 6.5
  check the CPU flag correctly
  opencv_visualization: check cmdline args
  provide better error messages
  stop search of markers in Exif reader to prevent infinite loop
  Fix calibration fail on python with CALIB_THIN_PRISM_MODEL flag
  clarify CUDA arithm operations usage with mask
  fixed empty image condition in resize
  fixed memory leak in flann tests
  fisheye: add CALIB_FIX_PRINCIPAL_POINT
  get/put: more type-safety and code unification using templates
  py_tutorials: fix cv2.findContours return val
  imgproc: speed up threshold of 64F version using NEON and SSE   * use NEON under aarch64 only   * check 64F version correctly
  bigdata: add test, resolve split/merge issue
  Improved Carotene library linear resize evaluation precision and enabled it as HAL implementation.
  persistence: fixing crash with space-only values
  Removed unnecessary check for Android API level and unused flags.
  Fix for median blur of 2-channel images
  ...

diff --cc modules/imgcodecs/src/grfmt_png.cpp
index 5b33c66,e672e0c..a7dae83
--- 1/modules/imgcodecs/src/grfmt_png.cpp
--- 2/modules/imgcodecs/src/grfmt_png.cpp
+++ b/modules/imgcodecs/src/grfmt_png.cpp
@@@ -230,9 -227,7 +230,7 @@@ bool  PngDecoder::readData( Mat& img 
      volatile bool result = false;
      AutoBuffer<uchar*> _buffer(m_height);
      uchar** buffer = _buffer;
 -    int color = img.channels() > 1;
 +    int color = img.channels() > 2;
-     uchar* data = img.ptr();
-     int step = (int)img.step;
  
      if( m_png_ptr && m_info_ptr && m_end_info && m_width && m_height )
      {