ue4: init at 4.10.2

This builds Unreal Engine 4 and has a wrapper to start the editor.

Sadly the application requires write access to a lot of paths. I have a
hack to do a symlink tree under $HOME and it works well, the UE4Editor
binary just needs to be not a symlink.

pkgs/games/ue4/generate-expr-from-cdn.sh

@@ -0,0 +1,37 @@
+#!/bin/sh
+
+go() {
+    file="$1"
+
+    IFS=$'\n'
+    for pack in $(perl -n -e '/(<Pack .*\/>)/ && print "$1\n"' $file); do
+        remotepath=$(echo "$pack" | perl -n -e '/RemotePath="([^"]*)"/ && print $1')
+        hash=$(echo "$pack" | perl -n -e '/Hash="([^"]*)"/ && print $1')
+        url="http://cdn.unrealengine.com/dependencies/$remotepath/$hash"
+
+        until sha256=$(nix-prefetch-url $url --type sha256); do
+            true
+        done
+
+        cat <<EOF
+  "$hash" = fetchurl {
+    url = $url;
+    sha256 = "$sha256";
+  };
+EOF
+    done
+}
+
+
+cat <<EOF
+{ fetchurl }:
+
+{
+EOF
+
+go Engine/Build/Commit.gitdeps.xml
+go Engine/Build/Promoted.gitdeps.xml
+
+cat <<EOF
+}
+EOF