[dev] Silver Theme

[Chuck Hagenbuch]

Quoting Jan Schneider <jan at horde.org>:

> This is a broader problem, because specifying inside a Horde file
> which modules provide a certain theme is a BC break in any case. I
> can't remember whether we discussed this when introducing
> $theme_icons. It's safer to check whether a theme directory exists
> inside an application's directory.

I don't think we did discuss it then. I agree that a directory check  
would be good to have.

-chuck