smartplaylist: Respect sort terms in queries
It would be nice to be able sort items in smart playlists, like so:

```
smartplaylist:
  relative_to: ~/music
  playlist_dir: ~/.mpd/playlists
  playlists:
    - name: '2014.m3u'
      query: 'year:2014 added+'
    - name: 'imported-%time{$added,%Y-%m}.m3u'
      query: "added:: path+"
```

I'm unfamiliar with the code but it looks like the smartplaylist plugin [discards the query `sort` field](https://github.com/sampsyo/beets/blob/master/beetsplug/smartplaylist.py#L45) when building playlists. Would it be possible to keep the custom sort?

diff --git a/beetsplug/smartplaylist.py b/beetsplug/smartplaylist.py
index 653a59d30..49a3c84de 100644
--- a/beetsplug/smartplaylist.py
+++ b/beetsplug/smartplaylist.py
@@ -18,7 +18,6 @@ from __future__ import print_function
 
 from beets.plugins import BeetsPlugin
 from beets import config, ui, library
-from beets import dbcore
 from beets.util import normpath, syspath
 import os
 
@@ -36,23 +35,21 @@ def _items_for_query(lib, playlist, album=False):
     if key not in playlist:
         return []
 
-    # Parse quer(ies). If it's a list, join the queries with OR.
+    # Parse quer(ies). If it's a list, perform the queries and manually
+    # concatenate the results
     query_strings = playlist[key]
     if not isinstance(query_strings, (list, tuple)):
         query_strings = [query_strings]
     model = library.Album if album else library.Item
-    query = dbcore.OrQuery(
-        [library.parse_query_string(q, model)[0] for q in query_strings]
-    )
-
-    # Execute query, depending on type.
-    if album:
-        result = []
-        for album in lib.albums(query):
-            result.extend(album.items())
-        return result
-    else:
-        return lib.items(query)
+    results = []
+    for q in query_strings:
+        querystr, sort = library.parse_query_string(q, model)
+        if album:
+            new = lib.albums(querystr, sort)
+        else:
+            new = lib.items(querystr, sort)
+        results.extend(new)
+    return results
 
 
 def update_playlists(lib):
['beetsplug/smartplaylist.py']