Path checks before download

[kneekoo]

Linux is very flexible with mounts and this is why Deluge has some issues with download paths. Let's take a look at a real case:

1. Start and finish a torrent on a mounted path, then close Deluge 2. Unmount that path (manually or by reboot) 3. Start Deluge again

The result is a new download from scratch. It will obviously have an impact on torrent ratio - wherever that counts.

Possible solution:

Check for the initial download path and if it doesn't exist pause the torrent and: 1. inform the user either by a message or mark the torrent with a different colour (light red?); 2. ask the user for a new download path and also present a Retry button so the user can mount that path and try again (and add a "Solve later" button); 3. create an option to switch between options #1 and #2 above because automatic start-ups will block Deluge from downloading if #2 is waiting for user input

[Cas]

If the path does not exist then Deluge will usually error or get 'stuck checking'. So Deluge should not be able to start the download again if the mount you have specified to download to is actually missing.

Anyway this is a Dup of #1032 and #491

#1294 is also relevant