[mythtv] first patch :) - mythweb image_cache

[Chris Petersen]

> i used file_exists instead of  is_file on purpose 
> since is_file generated errors on my system for files larger than 2gb

What are you doing with preview thumbnails more than 2G?  the image 
cache folder is *not* the recordings directory, you shouldn't have any 
recordings in there.

anyway, I used is_file on purpose -- I don't want it to delete symlinks, 
etc.

I've reordered things so that the regex comes before the is_file -- this 
should avoid problems with is_file.

-Chris