Stitch trunk ZODB into this branch using svn:externals

o setup.py:  Add support for building IFBTrees.

o XXX:  One test fails inside ZopeX3 code, because the contract for
        IDataManager just changed last week (it got accurately documented,
        actually).

setup.py

@@ -234,6 +234,10 @@ def __init__(self, attrs):
                   include_dirs=EXTENSIONCLASS_INCLUDEDIRS + ['persistent'],
                   define_macros=[('EXCLUDE_INTSET_SUPPORT', None)],
                   sources=['BTrees/_IIBTree.c']),
+        Extension(name='BTrees._IFBTree',
+                  include_dirs=EXTENSIONCLASS_INCLUDEDIRS + ['persistent'],
+                  define_macros=[('EXCLUDE_INTSET_SUPPORT', None)],
+                  sources=['BTrees/_IFBTree.c']),
         Extension(name='BTrees._IOBTree',
                   include_dirs=EXTENSIONCLASS_INCLUDEDIRS + ['persistent'],
                   define_macros=[('EXCLUDE_INTSET_SUPPORT', None)],