Port rev 27272 from 3.3 branch.

Empty BTrees/__init__.py; isn't doing anything except
creating problems.

NEWS.txt

@@ -2,6 +2,15 @@ What's new in ZODB3 3.3 ?
 =========================
 Release date: DD-MMM-YYYY
 
+BTrees
+------
+
+The BTrees __init__.py file is now just a comment.  It had been trying
+to set up support for (long gone) "int sets", and to import an old
+version of Zope's Interface package, which doesn't even ship with ZODB.
+The latter in particular created problems, at least clashing with
+PythonCAD's Interface package.
+
 Tools
 -----
 

src/BTrees/__init__.py

-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
+# This is a Python package.