Addressing @stesch13's timeout concerns

I raised the arbitrary-ish revocation timeout from 10ms to 500ms. I hope
to refine this value in the future with input from YOU, my users reading
this.

Please comment on this commit with any feedback you have.

@stesch13's concerns can be found at
https://github.com/eligrey/FileSaver.js/commit/485930a#commitcomment-8768047

FileSaver.js

@@ -1,6 +1,6 @@
 /* FileSaver.js
  * A saveAs() FileSaver implementation.
- * 2014-08-29
+ * 2014-11-29
  *
  * By Eli Grey, http://eligrey.com
  * License: X11/MIT
@@ -49,9 +49,10 @@ var saveAs = saveAs
 		}
 		, force_saveable_type = "application/octet-stream"
 		, fs_min_size = 0
-		// See https://code.google.com/p/chromium/issues/detail?id=375297#c7 for
-		// the reasoning behind the timeout and revocation flow
-		, arbitrary_revoke_timeout = 10
+		// See https://code.google.com/p/chromium/issues/detail?id=375297#c7 and
+		// https://github.com/eligrey/FileSaver.js/commit/485930a#commitcomment-8768047
+		// for the reasoning behind the timeout and revocation flow
+		, arbitrary_revoke_timeout = 500 // in ms
 		, revoke = function(file) {
 			var revoker = function() {
 				if (typeof file === "string") { // file is an object URL