#4 override poddir for specific feeds

[Rajesh Duggal]

A very very useful feature for Podracer would be to be able
to optionally specify a directory you want the feed files
to be downloaded to in the subscriptions file.

e.g. I might have five rss feeds in the subscriptions
file and I want all of files to go the directory specified by pod dir.. but for one of the feeds I want to override the setting and it go to a different directory.
This dir path could be specified with the feed in the
subscriptions file.

This additional feature would be backwards compatible with people's current subscription files.