Remove db requirement from constructor and add get_plural_relationship_string to relationship class.

svn: r8831

src/PluginUtils/_PluginMgr.py

@@ -467,9 +467,9 @@ def register_relcalc(relclass, languages):
     except:
         pass
 
-def relationship_class(db):
+def relationship_class():
     global _relcalc_class
-    return _relcalc_class(db)
+    return _relcalc_class()
 
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