importadded: Set added field before moving files

I have a collection that I organize according to year of purchase (or acquisition) and I want to import it to beets with the same hierarchy.

So I activated the importadded plugins and have the following path :

```
default: $format/%left{$mtime,4}/$albumartist - $album%aunique{}/$track $title
```

or (which should be better) :

```
default: $format/%left{$added,4}/$albumartist - $album%aunique{}/$track $title
```

so that I get (for an album that has mtime 2011) : MP3/2011/artist - album/01 title.mp3

This does not seem to work, the files are put in MP3/1970/artist...

After importing one test album I try out ```
$ beet ls -f '%left{$mtime,4} %left{$added,4} $artist $title'
2011 2011 artist title
[snip]

```

which seems correct. I guess the added or mtime is filled into the database later in the process, or is this another bug ?
```

Start by tracing the importadded plugin and the import/move sequence reproduced with the shown beet import and beet ls commands. Confirm whether $added and $mtime are set before the path template is evaluated; done means the imported album is placed under MP3/2011 and beet ls reports 2011 for both fields.

Written by the indexing model from the issue text.