[devel] Corrected const_png_ in png.h to png_const_ to avoid polluting

 the namespace.  Added png_get_current_row_number and
 png_get_current_pass_number for the
 benefit of the user transform callback.
 Added png_process_data_pause and png_process_data_skip for the benefit of
 progressive readers that need to stop data processing or want to optimize
 skipping of unread data (e.g. if the reader marks a chunk to be skipped.)
14 files changed