Only issue "From wrong source" for binaries not at the same version in testing

Same-version could happen for merged binaries in partial-unstable mode.

britney.py

@@ -1222,6 +1222,7 @@ class Britney(object):
             # if the new binary package is not from the same source as the testing one, then skip it
             # this implies that this binary migration is part of a source migration
             if source_u.version == pkgsv and source_t.version != pkgsv:
+                if binary_t is None or binary_t.version != binary_u.version:
                     anywrongver = True
                     excuse.addhtml("From wrong source: %s %s (%s not %s)" % (pkg_name, binary_u.version, pkgsv, source_t.version))
                     continue