@jeffkaufman I traced back my steps, and now see what happened here - I think I came to a wrong conclusion when testing this code, and might have hit an issue. 

It seems that the following is all that is required to enable IPRO:
```
http {
   ...
    pagespeed FileCachePath /tmp/psol_cache;
    server { 
    ...
    pagespeed InPlaceResourceOptimization on;
   }
}
```

When I tested this, I noticed that there was no `pagespeed on` in `pagespeed_test.conf.template` at the top level. I thought that the default was off, and with that concluded that `IPRO` could be enabled all by itself. Because when I requested a css for a vhost with only `pagespeed InPlaceResourceOptimization on;` I noticed attempts to write to the configured file system cache. 
Hence I proposed the option to also enable the gzip change for when IPRO is enabled to @keesspoelstra  - which now doesn't seem to make sense.

Our readme states that `pagespeed on;` is required, but testing makes it seem like all that is needed to enable pagespeed is a single line: `pagespeed FileSystemCache xxx;`
Is that by design? Or is this a bug?