Allow table/to-struct to take a prototype.

Use this prototype struct in freeze.

src/boot/boot.janet

@@ -2230,8 +2230,16 @@
     (tuple/slice (map freeze x))
 
     (or (= tx :table) (= tx :struct))
-    (let [sorted-kvs (array/join @[] ;(sort (map freeze (pairs x))))]
-      (struct/with-proto (freeze (getproto x)) ;sorted-kvs))
+    (let [temp-tab @{}]
+      # Handle multiple unique keys that freeze. Result should
+      # be independent of iteration order.
+      (eachp [k v] x
+        (def kk (freeze k))
+        (def vv (freeze v))
+        (def old (get temp-tab kk))
+        (def new (if (= nil old) vv (max vv old)))
+        (put temp-tab kk new))
+      (table/to-struct temp-tab (freeze (getproto x))))
 
     (= tx :buffer)
     (string x)

src/core/table.c

@@ -372,12 +372,14 @@ JANET_CORE_FN(cfun_table_setproto,
 }
 
 JANET_CORE_FN(cfun_table_tostruct,
-              "(table/to-struct tab)",
-              "Convert a table to a struct. Returns a new struct. This function "
-              "does not take into account prototype tables.") {
-    janet_fixarity(argc, 1);
+              "(table/to-struct tab &opt proto)",
+              "Convert a table to a struct. Returns a new struct.") {
+    janet_arity(argc, 1, 2);
     JanetTable *t = janet_gettable(argv, 0);
-    return janet_wrap_struct(janet_table_to_struct(t));
+    JanetStruct proto = janet_optstruct(argv, argc, 1, NULL);
+    JanetStruct st = janet_table_to_struct(t);
+    janet_struct_proto(st) = proto;
+    return janet_wrap_struct(st);
 }
 
 JANET_CORE_FN(cfun_table_rawget,