Warning about appcache getting fed standard cache

The `?rel=324784983` querystrings are misleading, this is NOT a reliable method of cache busting. (So I removed them) This is something the developer needs to know about and since grunt-contrib-manifest is only concerned with generating the manifest. However, grunt-contrib-manifest could match rails md5 hash algorithm to hit the right files, same thing with yeoman, and there could be a setting to add the file hash before or after the filename (but always before the extension of course) There could also be a setting to add the file hash at the root like: `domain.com/hash/actual/path/to/file.js` this scheme may be easier to support for say, node.js