sortable dates for file names on sync device

Signed-off-by: Rafi Rubin <rafi@seas.upenn.edu>

src/gpodder/config.py

@@ -166,7 +166,7 @@ defaults = {
 
         'max_filename_length': 999,
 
-        'custom_sync_name': '{episode.pubdate_prop}_{episode.title}',
+        'custom_sync_name': '{episode.sortdate}_{episode.title}',
         'custom_sync_name_enabled': False,
 
         'after_sync': {

src/gpodder/model.py

@@ -733,6 +733,10 @@ class PodcastEpisode(PodcastModelObject):
     
     pubdate_prop = property(fget=cute_pubdate)
 
+    @property
+    def sortdate(self):
+	    return str(datetime.datetime.fromtimestamp(self.published).strftime('%F'))
+
     def calculate_filesize(self):
         filename = self.local_filename(create=False)
         if filename is None: