Circumventing proxy caches of js and css files

The Problem:
Some ISPs have aggressive proxy caches that, by default cache js and css file for up to a month with no way of forcing a refresh. When the files are updates (Core or module update), end-users who with an aggressive cache will be served an old version of the css or js file.. This will eventually be fixed when the proxy refreshes its cache, but in the mean time, this breaks the site functionality and layout.

the solution:
A very easy way to circumvent this problem is to append a get request to the file name.. for example instead of including "drupal.js", include "drupal.js?xyz". Now, every time xyz changes, the caching proxy will think it is a different version of the file and fetch a fresh version..
Practically xyz can be either a version number or some kind of unique hash so that each time the file is changed the cache will be refreshed. Of course, as long as xyz stays the same, the file will be cached and bandwidth saved.

Other than getting a unique hash and appending it to the file request, nothing needs to be changed in the core.

This small change will enhance the drupal experience of all users and make updates go smoother.