use the LWN weekly publication date

Borrows a trick from foreignaffairs.recipe to set the publication date
in the title as opposed to the conversion date. Bulk conversion
(unfortunately) is a frequent thing when catching up after a holiday or
crontab breakage. It is really annoying figuring out the LWN weekly
edition reading order if they all have the same title based on the
conversion date.

recipes/lwn_weekly.recipe

@@ -91,6 +91,12 @@ class WeeklyLWN(BasicNewsRecipe):
         else:
             index_url = self.print_version('/free/bigpage')
         soup = self.index_to_soup(index_url)
+
+        date_match = re.match(r'.* +for +(.*) +\[.*', self.tag_to_string(
+            soup.head.title.string))
+        if date_match:
+            self.timefmt = u' [%s]' % date_match[1]
+
         curr = soup.body
 
         articles = {}