Try to fix a bunch of compiler warnings on Win64.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 68df57d..5dd89c4 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -7261,7 +7261,7 @@
             done = str->length;
 	}
 	while (done < nchars) {
-            int n = (done <= nchars-done) ? done : nchars-done;
+            Py_ssize_t n = (done <= nchars-done) ? done : nchars-done;
             Py_UNICODE_COPY(p+done, p, n);
             done += n;
 	}