update_nacl_manifest improvements

native_client_sdk/src/build_tools/json/naclsdk_manifest2.json

 {
   "bundles": [
     {
       "name": "sdk_tools",
       "description": "Native Client SDK Tools, revision 160493",
       "stability": "stable",
       "recommended": "yes",
       "version": 1,
       "archives": [
         {
@@ skipping 43 matching lines @@
     },
     {
       "name": "vs_addin",
       "description": "Visual Studio Add-In for building and debugging NaCl applications",
       "stability": "dev",
       "recommended": "no",
       "version": 0,
       "repath": "vs_addin",
       "archives": [
         {
-          "url": "https://commondatastorage.googleapis.com/nativeclient-mirror/nacl/nacl_sdk/sdk/1449/vs_addin.tgz",
-          "checksum": {
-            "sha1": "91acaf2535ad8b464a799af5251197bab02869ee"
-          },
-          "host_os": "win",
-          "size": 86759
+          "url": "https://commondatastorage.googleapis.com/nativeclient-mirror/nacl/nacl_sdk/sdk/${revision}/vs_addin.tgz",
+          "host_os": "win"
         }
       ],
       "revision": 1449
     },
     {
       "name": "pepper_16",
       "description": "Chrome 16 bundle, revision 1398",
       "stability": "post_stable",
       "recommended": "no",
       "version": 16,
@@ skipping 175 matching lines @@
       "stability": "canary",
       "recommended": "no",
       "version": 0,
       "repath": "",
       "archives": [],
       "revision": 0
     }
   ],
   "manifest_version": 2
 }