models: Don't query a related field in __unicode__

Turns out that str(object) is used when putting 'object' in the
template context. Because of revisions __unicode__ was using series.name
we were doing as many queries as revisions in the detailed series page,
without actually using that string representation anywhere.

Because the string representation of SeriesRevision is not very useful,
let's just get rid of that query altogether.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

patchwork/models.py

@@ -533,10 +533,7 @@ def duplicate(self, exclude_patches=()):
         return new
 
     def __unicode__(self):
-        if hasattr(self, 'series'):
-            return self.series.name + " (rev " + str(self.version) + ")"
-        else:
-            return "New revision" + " (rev " + str(self.version) + ")"
+        return "Revision " + self.version
 
 class SeriesRevisionPatch(models.Model):
     patch = models.ForeignKey(Patch)