Make identifiers str (not str8) objects throughout.
This affects the parser, various object implementations,
and all places that put identifiers into C string literals.

In testing, a number of crashes occurred as code would
fail when the recursion limit was reached (such as the
Unicode interning dictionary having key/value pairs where
key is not value). To solve these, I added an overflowed
flag, which allows for 50 more recursions after the
limit was reached and the exception was raised, and
a recursion_critical flag, which indicates that recursion
absolutely must be allowed, i.e. that a certain call
must not cause a stack overflow exception.

There are still some places where both str and str8 are
accepted as identifiers; these should eventually be
removed.
diff --git a/Objects/descrobject.c b/Objects/descrobject.c
index e9ccefa..acd2400 100644
--- a/Objects/descrobject.c
+++ b/Objects/descrobject.c
@@ -15,7 +15,10 @@
 static char *
 descr_name(PyDescrObject *descr)
 {
-	if (descr->d_name != NULL && PyString_Check(descr->d_name))
+	if (descr->d_name != NULL && PyUnicode_Check(descr->d_name))
+		return PyUnicode_AsString(descr->d_name);
+	else if (descr->d_name != NULL && PyString_Check(descr->d_name))
+		/* XXX this should not happen */
 		return PyString_AS_STRING(descr->d_name);
 	else
 		return "?";
@@ -581,7 +584,7 @@
 	if (descr != NULL) {
 		Py_XINCREF(type);
 		descr->d_type = type;
-		descr->d_name = PyString_InternFromString(name);
+		descr->d_name = PyUnicode_InternFromString(name);
 		if (descr->d_name == NULL) {
 			Py_DECREF(descr);
 			descr = NULL;