message: dshow: Only show debugging messages if environment variable OPENCV_DSHOW_DEBUG is explicitly set to non-zero
  Based on discussion at:
diff: @@ -337,11 +337,17 @@ interface ISampleGrabber : public IUnknown
  #ifdef _DEBUG
  #include <strsafe.h>
  -//change for verbose debug info
  -static bool gs_verbose = true;
  -
  static void DebugPrintOut(const char *format, ...)
  {
  + static int gs_verbose = -1;
  + if (gs_verbose < 0)
  + {
  + // Fetch initial debug state from environment - defaults to disabled
  + const char* s = getenv("OPENCV_DSHOW_DEBUG");
  + gs_verbose = s != NULL && atoi(s) != 0;
  + }
  +
  +
  if (gs_verbose)
  {
  va_list args;
  @@ -487,9 +493,6 @@ class videoInput{
  videoInput();
  ~videoInput();
  - //turns off console messages - default is to print messages
  - static void setVerbose(bool _verbose);
  -
  //Functions in rough order they should be used.
  static int listDevices(bool silent = false);
  @@ -1120,20 +1123,6 @@ videoInput::videoInput(){
  }
  -
  -// ----------------------------------------------------------------------
  -// static - set whether messages get printed to console or not
  -//
  -// ----------------------------------------------------------------------
  -
  -void videoInput::setVerbose(bool _verbose){
  -#ifdef _DEBUG
  - gs_verbose = _verbose;
  -#else
  - (void)_verbose; // Suppress 'unreferenced parameter' warning
  -#endif
  -}
  -
  // ----------------------------------------------------------------------
  // change to use callback or regular capture
  // callback tells you when a new frame has arrived
  