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/Python/sysmodule.c b/Python/sysmodule.c
index 30e0180..1b7674b 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -280,7 +280,7 @@
 	int i;
 	for (i = 0; i < 7; ++i) {
 		if (whatstrings[i] == NULL) {
-			name = PyString_InternFromString(whatnames[i]);
+			name = PyUnicode_InternFromString(whatnames[i]);
 			if (name == NULL)
 				return -1;
 			whatstrings[i] = name;
@@ -801,7 +801,7 @@
 	if (list == NULL)
 		return NULL;
 	for (i = 0; PyImport_Inittab[i].name != NULL; i++) {
-		PyObject *name = PyString_FromString(
+		PyObject *name = PyUnicode_FromString(
 			PyImport_Inittab[i].name);
 		if (name == NULL)
 			break;