Fix Repo comparison on Python 2

Python 3 automatically defines the right __ne__ if you define an __eq__,
but Python 2 doesn't.

The comparison operators are only used in unit tests so this is not a
user-visible bug.

ghcloneall.py

@@ -363,6 +363,9 @@ def __eq__(self, other):
             other.name, other.clone_url, other.urls,
         )
 
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
     @classmethod
     def from_repo(cls, repo):
         # use repo['git_url'] for anonymous checkouts, but they'e slower

tests.py

@@ -666,8 +666,11 @@ def test_Repo():
     r3 = ghcloneall.Repo('bar', 'git@github.com:test_user/bar.git',
                          ['https://github.com/test_user/bar'])
     assert r1 == r2
+    assert not r1 != r2
     assert r1 != r3
+    assert not r1 == r3
     assert r1 != 'foo'
+    assert not r1 == 'foo'
     assert repr(r1) == (
         "Repo('foo', 'git@github.com:test_user/foo.git',"
         " {'git@github.com:test_user/foo.git',"