backport r62271 from trunk.
remove the now obsoleted assertion.
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index 7cd613d..3901f57 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -53,7 +53,6 @@
 PyString_FromStringAndSize(const char *str, Py_ssize_t size)
 {
 	register PyStringObject *op;
-	assert(size >= 0);
 	if (size < 0) {
 		PyErr_SetString(PyExc_SystemError,
 		    "Negative size passed to PyString_FromStringAndSize");