Add restrictedGlobals option

Keep from undesirable global variable assignment by configuration.

For example, underscore.string redefines "window._" if it is undefined, to
assign "window._.str".

    if (typeof root._ !== "undefined") {
       ...
   } else {
       root._ = { str : ... };
   }

Inference engine thinks "window._" assigned twice in this case. For
workaround, manually restricts global assignment to specific file by below
config.

    "restrictedGlobals" : {
       "_" : "lib/underscore.js"
   }

(Also accepts list of filenames.)


I found {"libs" : "underscore"} config works fine.
But I'm sending this request because perhaps there are other modules
affects, or some one want to use the real module to follow latest /
remain legacy one.


Thank you for creating great product :)