The following patch adds "sq_contains" support to rangeobject, and enables
the already-written support for sq_contains in listobject and tupleobject.

The rangeobject "contains" code should be a bit more efficient than the
current default "in" implementation ;-) It might not get used much, but it's
not that much to add.

listobject.c and tupleobject.c already had code for sq_contains, and the
proper struct member was set, but the PyType structure was not extended to
include tp_flags, so the object-specific code was not getting called (Go
ahead, test it ;-). I also did this for the immutable_list_type in
listobject.c, eventhough it is probably never used. Symmetry and all that.