Revert "Make png_uint_32 32 bits wide on all platforms."

This reverts commit 98b7535d85203c12a1989a66e958baf9dbc475c4.
diff --git a/pngconf.h b/pngconf.h
index d0dc20c..219b42e 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1236,8 +1236,8 @@
  * want to have unsigned int for png_uint_32 instead of unsigned long.
  */
 
-typedef unsigned int png_uint_32;
-typedef int png_int_32;
+typedef unsigned long png_uint_32;
+typedef long png_int_32;
 typedef unsigned short png_uint_16;
 typedef short png_int_16;
 typedef unsigned char png_byte;