tests: make test-manifest finish importing in Python 3

The test is still broken, but now it executes.

tests/test-manifest.py

@@ -92,9 +92,13 b' A_DEEPER_MANIFEST = ('
 
 HUGE_MANIFEST_ENTRIES = 200001
 
+izip = getattr(itertools, 'izip', zip)
+if 'xrange' not in globals():
+    xrange = range
+
 A_HUGE_MANIFEST = ''.join(sorted(
     'file%d\0%s%s\n' % (i, h, f) for i, h, f in
-    itertools.izip(xrange(200001),
+    izip(xrange(200001),
                    itertools.cycle((HASH_1, HASH_2)),
                    itertools.cycle(('', 'x', 'l')))))