param: Present alias names to tweaks

Instead of simply resolving the original parameter and passing it on
pristine to its tweak, build an intermediary param spec that has all
the properties of the original with the name of the alias.

This enables special handling of deprecated aliases with their
replacements.

bin/varnishd/mgt/mgt_param_tweak.c

@@ -565,9 +565,15 @@ tweak_storage(struct vsb *vsb, const struct parspec *par, const char *arg)
 int v_matchproto_(tweak_t)
 tweak_alias(struct vsb *vsb, const struct parspec *par, const char *arg)
 {
-
-	par = TRUST_ME(par->priv);
-	return (par->func(vsb, par, arg));
+	const struct parspec *orig;
+	struct parspec alias[1];
+
+	orig = TRUST_ME(par->priv);
+	AN(orig);
+	memcpy(alias, orig, sizeof *orig);
+	alias->name = par->name;
+	alias->priv = TRUST_ME(orig);
+	return (alias->func(vsb, alias, arg));
 }
 
 /*--------------------------------------------------------------------