add attribute-based mechanism to disable rewriting a resource.

```
We can currently disable defer_javascript via HTML attribute 
'pagespeed_no_defer'.  Similarly, we should be able to disable the optimization 
of any HTML tag by a similar mechanism in the markup.  Disabling via a Disallow 
wildcard might be difficult to maintain as sites change.

```

Original issue reported on code.google.com by `jmara...@google.com` on 10 Oct 2012 at 7:24
