revision.h: store hidden refs in a strvec

In subsequent commits, it will be convenient to have a 'const char **'
of hidden refs (matching `transfer.hiderefs`, `uploadpack.hideRefs`,
etc.), instead of a `string_list`.

Convert spots throughout the tree that store the list of hidden refs
from a `string_list` to a `strvec`.

Note that in `parse_hide_refs_config()` there is an ugly const-cast used
to avoid an extra copy of each value before trimming any trailing slash
characters. This could instead be written as:

    ref = xstrdup(value);
    len = strlen(ref);
    while (len && ref[len - 1] == '/')
            ref[--len] = '\0';
    strvec_push(hide_refs, ref);
    free(ref);

but the double-copy (once when calling `xstrdup()`, and another via
`strvec_push()`) is wasteful.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -1427,7 +1427,7 @@ char *shorten_unambiguous_ref(const char *refname, int strict)
 }
 
 int parse_hide_refs_config(const char *var, const char *value, const char *section,
-			   struct string_list *hide_refs)
+			   struct strvec *hide_refs)
 {
 	const char *key;
 	if (!strcmp("transfer.hiderefs", var) ||
@@ -1438,22 +1438,23 @@ int parse_hide_refs_config(const char *var, const char *value, const char *secti
 
 		if (!value)
 			return config_error_nonbool(var);
-		ref = xstrdup(value);
+
+		/* drop const to remove trailing '/' characters */
+		ref = (char *)strvec_push(hide_refs, value);
 		len = strlen(ref);
 		while (len && ref[len - 1] == '/')
 			ref[--len] = '\0';
-		string_list_append_nodup(hide_refs, ref);
 	}
 	return 0;
 }
 
 int ref_is_hidden(const char *refname, const char *refname_full,
-		  const struct string_list *hide_refs)
+		  const struct strvec *hide_refs)
 {
 	int i;
 
 	for (i = hide_refs->nr - 1; i >= 0; i--) {
-		const char *match = hide_refs->items[i].string;
+		const char *match = hide_refs->v[i];
 		const char *subject;
 		int neg = 0;
 		const char *p;