+the previous current pad. NB currently this macro expands to a string too
+long for some compilers, so it's best to replace it with
+
+ SAVECOMPPAD();
+ PAD_SET_CUR_NOSAVE(padlist,n);
+
+
+=for apidoc m|void|PAD_SET_CUR_NOSAVE |PADLIST padlist|I32 n
+like PAD_SET_CUR, but without the save