[pngzop] Added pngidat script and pngidat.c, and updated references to

include pigz

pngidat.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+
+/* Copyright 2013 Glenn Randers-Pehrson */
+
+/* Usage:            
+ * pngidat.exe < file.png | pigz -d > file.idat
+ *
+ * file.idat is the image datastream, with the filter bytes.
+ */
+
+main()
+{
+   int i;
+   int buf[5];
+   int c;
+
+   buf[4]='\0';
+
+/* Skip 8-byte signature */
+   for (i=8; i; i--)
+      c=getchar();
+
+for (;;)
+{
+   /* read length */
+   int length;
+   buf[0]=getchar();
+   if (buf[0] == EOF)
+      break;
+   buf[1]=getchar();
+   buf[2]=getchar();
+   buf[3]=getchar();
+   length=buf[0]<<24 | buf[1]<<16 | buf[2] << 8 | buf[3];
+   /* read chunkname */
+   buf[0]=getchar();
+   buf[1]=getchar();
+   buf[2]=getchar();
+   buf[3]=getchar();
+   if (buf[0] == 'I' && buf[1] == 'D' && buf[2] == 'A' && buf[3] == 'T')
+   {
+      /* copy the data bytes */
+      for (i=length; i; i--)
+      {
+         c=getchar();
+         if (c == EOF)
+            break;
+         putchar(c);
+      }
+      /* skip crc byte */
+      for (i=4; i; i--)
+      {
+         c=getchar();
+      }
+   }
+
+   else if (buf[0] == 'I' && buf[1] == 'E' && buf[2] == 'N' && buf[3] == 'D')
+     break;
+
+   else
+   {
+      for (i=length+4; i; i--)
+         c=getchar();
+   }
+}
+}