* Fetchurl: check md5 checksum.

corepkgs/fetchurl/fetchurl.fix

-Function(["url", "hash"],
+Function(["url", "md5"],
   Package(
     [ ("build", Relative("fetchurl/fetchurl.sh"))
     , ("url", Var("url"))
-    , ("hash", Var("hash"))
+    , ("md5", Var("md5"))
     , ("name", BaseName(Var("url")))
     ]
   )

corepkgs/fetchurl/fetchurl.sh

 #! /bin/sh
 
-wget "$url" -O "$out"
+echo "downloading $url into $out..."
+wget "$url" -O "$out" || exit 1
+
+actual=$(md5sum -b $out | cut -c1-32)
+if ! test "$actual" == "$md5"; then
+    echo "hash is $actual, expected $md5"
+    exit 1
+fi