[Seaside] FileLibrary / css files confusion - red herring :-(

[itsme213]

The problem embarassingly turned out to be browser caching. The only way to 
turn this off in Firefox is through
    about:config
    ---  network.http.use-cache = false

Changing the base url had the effect of invalidating that cache, so I 
incorrectly thought that hacking '/seaside/' somehow caused the problem.

I am back in business with the strictly unsupported '/seaside/' hack, far 
slower page loads, and reliable css-updates.

Thanks Lukas, Keith, Amos.