Added code to get the interfaces registered with the OOBTree classes.

Eventually, we should add registration for the other flavors too.
This will require deciding how to specify the II, IO, OI variants. ;)

src/BTrees/__init__.py

@@ -3,3 +3,11 @@ import ZODB
 try: import intSet
 except: pass
 else: del intSet
+
+# Register interfaces
+try: import Interface
+except ImportError: pass # Don't register interfaces if no scarecrow
+else:
+    import Interfaces
+    del Interfaces
+    del Interface