[master] Added macros to detect use of deprecated features.

Added PNG_DEPSTRUCT, PNG_DEPRECATED, PNG_USE_RESULT, PNG_NORETURN, and
    PNG_ALLOCATED macros to detect deprecated direct access to the
    png_struct or info_struct members and other deprecated usage in
    applications (John Bowler).
  Added -DPNG_CONFIGURE_LIBPNG to the makefile CFLAGS, to prevent warnings
    about direct access to png structs by libpng functions while building
    libpng.
  Removed three direct references to read_info_ptr members in pngtest.c
    that were detected by the new PNG_DEPSTRUCT macro.
  Moved the png_debug macro definitions and the png_read_destroy(),
    png_write_destroy() and png_far_to_near() prototypes from png.h
    to pngpriv.h (John Bowler)
  Moved the synopsis lines for png_read_destroy(), png_write_destroy()
    png_debug(), png_debug1(), and png_debug2() from libpng.3 to libpngpf.3.

pngerror.c

@@ -22,7 +22,7 @@
 
 static void /* PRIVATE */
 png_default_error PNGARG((png_structp png_ptr,
-  png_const_charp error_message));
+  png_const_charp error_message)) PNG_NORETURN;
 #ifdef PNG_WARNINGS_SUPPORTED
 static void /* PRIVATE */
 png_default_warning PNGARG((png_structp png_ptr,
@@ -285,9 +285,9 @@ png_default_error(png_structp png_ptr, png_const_charp error_message)
    longjmp(png_ptr->jmpbuf, 1);
 #  endif
    }
-#else
-   PNG_ABORT();
 #endif
+   /* Here if not setjmp support or if png_ptr is null. */
+   PNG_ABORT();
 #ifndef PNG_CONSOLE_IO_SUPPORTED
    error_message = error_message; /* Make compiler happy */
 #endif