[devel]  Moved "#include png.h" inside pngpriv.h and removed "#include png.h"

from the source files, along with "#define PNG_EXPOSE_INTERNAL_STRUCTURES"
and "#define PNG_NO_PEDANTIC_WARNINGS" (John Bowler).
Also created new pngdebug.h and moved debug definitions there.
diff --git a/pngwtran.c b/pngwtran.c
index bda4a63..0f9644a 100644
--- a/pngwtran.c
+++ b/pngwtran.c
@@ -11,12 +11,10 @@
  * and license in png.h
  */
 
-#define PNG_EXPOSE_INTERNAL_STRUCTURES
-#define PNG_NO_PEDANTIC_WARNINGS
-#include "png.h"
-#ifdef PNG_WRITE_SUPPORTED
 #include "pngpriv.h"
 
+#ifdef PNG_WRITE_SUPPORTED
+
 /* Transform the data according to the user's wishes.  The order of
  * transformations is significant.
  */