In cover/artist dialog, when attempting to save an image into Cantata's cache folder - ensure the 'covers' sub-folder is created.


git-svn-id: http://cantata.googlecode.com/svn/trunk@4235 b1e49159-3266-923f-9c3e-04f16369770a
When saving artist image from cover dialog, if set to save in MPD folder and song's path does not have 2 folder elements then save in cache folder. 
Cantata will only save artist images, and backdrops, in MPD folder if the folder structure is (e.g.) Artist/Album/Track.mp3
BUG: 429


git-svn-id: http://cantata.googlecode.com/svn/trunk@4236 b1e49159-3266-923f-9c3e-04f16369770a