backout https://github.com/vim/vim/commit/bd4614f43d0eac4aff743132bab8e53b015ac801.patch
segfaults seen, at least when using vim-airline

Index: src/filepath.c
--- src/filepath.c.orig
+++ src/filepath.c
@@ -670,14 +670,12 @@ repeat:
 			str = vim_strnsave(*fnamep, *fnamelen);
 			if (sub != NULL && str != NULL)
 			{
-			    size_t slen;
-
 			    *usedlen = p + 1 - src;
-			    s = do_string_sub(str, *fnamelen, pat, sub, NULL, flags, &slen);
+			    s = do_string_sub(str, pat, sub, NULL, flags);
 			    if (s != NULL)
 			    {
 				*fnamep = s;
-				*fnamelen = slen;
+				*fnamelen = (int)STRLEN(s);
 				vim_free(*bufp);
 				*bufp = s;
 				didit = TRUE;