patch 7.4.2072
Problem: substitute() does not support a Funcref argument.
Solution: Support a Funcref like it supports a string starting with "\=".
diff --git a/src/proto/regexp.pro b/src/proto/regexp.pro
index 5cdabb2..dfe5c91 100644
--- a/src/proto/regexp.pro
+++ b/src/proto/regexp.pro
@@ -7,7 +7,7 @@
reg_extmatch_T *ref_extmatch(reg_extmatch_T *em);
void unref_extmatch(reg_extmatch_T *em);
char_u *regtilde(char_u *source, int magic);
-int vim_regsub(regmatch_T *rmp, char_u *source, char_u *dest, int copy, int magic, int backslash);
+int vim_regsub(regmatch_T *rmp, char_u *source, typval_T *expr, char_u *dest, int copy, int magic, int backslash);
int vim_regsub_multi(regmmatch_T *rmp, linenr_T lnum, char_u *source, char_u *dest, int copy, int magic, int backslash);
char_u *reg_submatch(int no);
list_T *reg_submatch_list(int no);