Follow redirects when checking for the existence of MANIFEST.bz2

If we don't follow redirects, we might think that MANIFEST.bz2 exists
just because the HEAD request succeeds on the redirector URI.

scripts/nix-pull.in

@@ -50,7 +50,7 @@ sub processURL {
     my $manifest;
 
     # First see if a bzipped manifest is available.
-    if (system("$Nix::Config::curl --fail --silent --head '$url'.bz2 > /dev/null") == 0) {
+    if (system("$Nix::Config::curl --fail --silent --location --head '$url'.bz2 > /dev/null") == 0) {
         print "fetching list of Nix archives at `$url.bz2'...\n";
         $manifest = downloadFile "$url.bz2";
     }