list_inplace_concat() is now expressed in terms of list_extend() which avoids creating an intermediate tuple for iterable arguments other than lists or tuples.
list_inplace_concat() is now expressed in terms of list_extend() which
avoids creating an intermediate tuple for iterable arguments other than
lists or tuples.

In other words, a+=b no longer requires extra memory when b is not a
list or tuple.  The list and tuple cases are unchanged.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator