Use the key= argument to sorted()

cmp is gone in python3.  Also add a sorting method to Excuse that is
compatible with its __eq__/__hash__ methods.

Signed-off-by: Julien Cristau <jcristau@debian.org>

britney.py

@@ -1623,7 +1623,7 @@ class Britney(object):
             self.excuses.append(excuse)
 
         # sort the excuses by daysold and name
-        self.excuses.sort(key=attrgetter('daysold', 'name'))
+        self.excuses.sort(key=lambda x: x.sortkey())
 
         # extract the not considered packages, which are in the excuses but not in upgrade_me
         unconsidered = [e.name for e in self.excuses if e.name not in upgrade_me]

excuse.py

@@ -62,6 +62,11 @@ class Excuse(object):
         self.reason = {}
         self.htmlline = []
 
+    def sortkey(self):
+        if self.daysold == None:
+            return (-1, self.name)
+        return (self.daysold, self.name)
+
     @property
     def is_valid(self):
         return self._is_valid
@@ -144,7 +149,7 @@ class Excuse(object):
         for x in self.htmlline:
             res = res + "<li>" + x + "\n"
         lastdep = ""
-        for x in sorted(self.deps, lambda x,y: cmp(x.split('/')[0], y.split('/')[0])):
+        for x in sorted(self.deps, key=lambda x: x.split('/')[0]):
             dep = x.split('/')[0]
             if dep == lastdep: continue
             lastdep = dep
@@ -196,7 +201,7 @@ class Excuse(object):
         for x in self.htmlline:
             res.append("" + x + "")
         lastdep = ""
-        for x in sorted(self.deps, lambda x,y: cmp(x.split('/')[0], y.split('/')[0])):
+        for x in sorted(self.deps, key=lambda x: x.split('/')[0]):
             dep = x.split('/')[0]
             if dep == lastdep: continue
             lastdep = dep