Disallow .git entries in trees, like C git.

dulwich/objects.py

@@ -1014,7 +1014,7 @@ class Tree(ShaFile):
         for name, mode, sha in parse_tree(b''.join(self._chunked_text),
                                           True):
             check_hexsha(sha, 'invalid sha %s' % sha)
-            if b'/' in name or name in (b'', b'.', b'..'):
+            if b'/' in name or name in (b'', b'.', b'..', b'.git'):
                 raise ObjectFormatException('invalid name %s' % name)
 
             if mode not in allowed_modes:

dulwich/tests/test_objects.py

@@ -887,6 +887,7 @@ class TreeTests(ShaFileCheckTests):
         self.assertCheckFails(t, b'100644 .\0' + sha)
         self.assertCheckFails(t, b'100644 a/a\0' + sha)
         self.assertCheckFails(t, b'100644 ..\0' + sha)
+        self.assertCheckFails(t, b'100644 .git\0' + sha)
 
         # modes
         self.assertCheckSucceeds(t, b'100644 a\0' + sha)