add npm "tar" package for use by engine

admin/generate-dev-bundle.sh

@@ -98,6 +98,7 @@ npm install keypress@0.1.0
 npm install sockjs@0.3.4
 npm install http-proxy@0.8.5
 npm install underscore@1.4.2
+npm install tar@0.1.14
 
 # progress 0.1.0 has a regression where it opens stdin and thus does not
 # allow the node process to exit cleanly. See