Write permission errors

[JanzenJohn]

There should be an indication of deluge not having write access to the directory it is supposed to be downloading to, instead of just not starting.

Right now it just seems like the download just went stale, which leaves the user to wait, instead of checking if the directory has write access

[DjLegolas]

Just tested on the develop branch, and tried to download to /root as a normal user.
Got and error in the Status tab: Error: Permission denied and the torrent is in an error state.