vim-patch:8.1.0515: reloading a script gives errors for existing functions

Problem:    Reloading a script gives errors for existing functions.
Solution:   Allow redefining a function once when reloading a script.
ded5f1bed7

src/nvim/eval/typval.h

@@ -256,6 +256,7 @@ typedef int scid_T;
 // the line number in the script "sc_sid".
 typedef struct {
   scid_T sc_sid;     // script ID
+  int sc_seq;        // sourcing sequence number
   linenr_T sc_lnum;  // line number
 } sctx_T;