Write annotated package.json data back to package.json

Mostly so that we can use the _from data in shrinkwrap and ls later.

lib/install.js

@@ -715,6 +715,9 @@ function write (target, targetFolder, context, cb_) {
   chain
     ( [ [ cache.unpack, target.name, target.version, targetFolder
         , null, null, user, group ]
+      , [ fs, "writeFile"
+        , path.resolve(targetFolder, "package.json")
+        , JSON.stringify(target, null, 2) + "\n" ]
       , [ lifecycle, target, "preinstall", targetFolder ] ]
 
     // nest the chain so that we can throw away the results returned