Add __str__ method to debian_linux.debian.Version

Python 2.x does not use the __unicode__ method to implement str() or
string formatting with %s.  Add a __str__ method as a wrapper.

svn path=/dists/trunk/linux/; revision=20180

debian/lib/python/debian_linux/debian.py

@@ -85,6 +85,9 @@ $
     def __unicode__(self):
         return self.complete
 
+    def __str__(self):
+        return unicode(self).encode('utf-8')
+
     @property
     def complete(self):
         if self.epoch is not None: