patch 7.4.1228
Problem:    copy() and deepcopy() fail with special variables. (Nikolai
            Pavlov)
Solution:   Make it work.  Add a test.  Closes #614.
diff --git a/src/eval.c b/src/eval.c
index a4f5531..4c530a0 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -21939,6 +21939,7 @@
 #endif
 	case VAR_STRING:
 	case VAR_FUNC:
+	case VAR_SPECIAL:
 	    copy_tv(from, to);
 	    break;
 	case VAR_LIST: