Fix build with png-1.5.

--- src/glpng.c.orig	Mon Jul 10 21:27:10 2000
+++ src/glpng.c	Sun Jun  2 16:55:55 2013
@@ -29,7 +29,7 @@
 #include <GL/gl.h>
 #include <stdlib.h>
 #include <math.h>
-#include "png/png.h"
+#include <png.h>
 
 /* Used to decide if GL/gl.h supports the paletted extension */
 #ifdef GL_COLOR_INDEX1_EXT
@@ -276,7 +276,7 @@ int APIENTRY pngLoadRawF(FILE *fp, pngRawInfo *pinfo) 
 	endinfo = png_create_info_struct(png);
 
 	// DH: added following lines
-	if (setjmp(png->jmpbuf))
+	if (setjmp(png_jmpbuf(png)))
 	{
 		png_destroy_read_struct(&png, &info, &endinfo);
 		return 0;
@@ -380,7 +380,7 @@ int APIENTRY pngLoadF(FILE *fp, int mipmap, int trans,
 	endinfo = png_create_info_struct(png);
 
 	// DH: added following lines
-	if (setjmp(png->jmpbuf))
+	if (setjmp(png_jmpbuf(png)))
 	{
 		png_destroy_read_struct(&png, &info, &endinfo);
 		return 0;
@@ -559,7 +559,7 @@ int APIENTRY pngLoadF(FILE *fp, int mipmap, int trans,
 			#define ALPHA *q
 
 			switch (trans) {
-				case PNG_CALLBACK:
+				case PNG_CALLBACKT:
 					FORSTART
 						ALPHA = AlphaCallback((unsigned char) r, (unsigned char) g, (unsigned char) b);
 					FOREND
