Fix wrong height of pictures on x86_64

On 64-bit Fedora latex2rtf produced RTFs with insanely large pictures.
The dimensions of a PNG are stored in the header as 4-byte values.
GetPngSize() reads them as consecutive unsigned longs.
The problem is that sizeof(unsigned long) != 4 bytes. It's 8 bytes on
x86_64 Linux.
Use standard ISO C uint32_t instead.
With this patch the figures have their normal size.

Index: graphics.c
===================================================================
--- graphics.c	(revision 894)
+++ graphics.c	(working copy)
@@ -29,6 +29,7 @@
 #include <ctype.h>
 #include <limits.h>
 #include <math.h>
+#include <stdint.h>
 #ifdef UNIX
 #include <unistd.h>
 #endif
@@ -755,7 +756,7 @@
 
 static unsigned char * getPngChunk(FILE *fp, char *s)
 {
-	unsigned long size, crc;
+	uint32_t size, crc;
 	char head[5];
 	unsigned char *data;
 	
@@ -777,7 +778,7 @@
 
 		if (strcmp(head,"IEND") == 0) return NULL;
 		
-		diagnostics(6,"found chunk '%s' size %ld bytes",head,size);
+		diagnostics(6,"found chunk '%s' size %ld bytes",head,(unsigned long)size);
 		data = malloc(size);
 		if (data == NULL) return NULL;
 		
@@ -798,7 +799,7 @@
 static void GetPngSize(char *s, unsigned long *w, unsigned long *h, unsigned long *xres, unsigned long *yres, int *bad_res)
 {
     FILE *fp;
-    unsigned long *p;
+    uint32_t *p;
     unsigned char buffer[16];
     char reftag[9] = "\211PNG\r\n\032\n";
     unsigned char *data = NULL;
@@ -833,7 +834,7 @@
         return;
 	}
 
-	p = (unsigned long *) data;	
+	p = (uint32_t *) data;
 	*w = (g_little_endian) ? LETONL(*p) : *p;
 	p++;
 	*h = (g_little_endian) ? LETONL(*p) : *p;
@@ -846,7 +847,7 @@
         return;
 	}
 
-	p = (unsigned long *) data;	
+	p = (uint32_t *) data;
 	*xres = (g_little_endian) ? LETONL(*p) : *p;
 	p++;
 	*yres = (g_little_endian) ? LETONL(*p) : *p;