Use default urgency for all packages if Urgencies is missing.

britney.py

@@ -766,6 +766,7 @@ class Britney(object):
         urgencies = {}
         filename = os.path.join(basedir, "Urgency")
         self.__log("Loading upload urgencies from %s" % filename)
+        try:
             for line in open(filename):
                 l = line.split()
                 if len(l) != 3: continue
@@ -791,6 +792,8 @@ class Britney(object):
 
                 # update the urgency for the package
                 urgencies[l[0]] = l[2]
+        except IOError:
+            self.__log("%s missing; using default for all packages" % filename)
 
         return urgencies