fixed a rdonly flag bug in moo_shallowcpy()

added SequenceableCollection>>swap:with:

moo/lib/exec.c

@@ -3800,6 +3800,7 @@ static pf_t pftab[] =
 	{ "Apex_basicShiftFrom:to:count:",         { moo_pf_basic_shift,                      3, 3 } },
 	{ "Apex_basicSize",                        { moo_pf_basic_size,                       0, 0 } },
 	{ "Apex_class",                            { moo_pf_class,                            0, 0 } },
+	{ "Apex_copy",                             { moo_pf_shallow_copy,                     0, 0 } },
 	{ "Apex_hash",                             { pf_hash,                                 0, 0 } },
 	{ "Apex_isKindOf:",                        { moo_pf_is_kind_of,                       1, 1, } },
 	{ "Apex_perform",                          { pf_perform,                              1, MA } },

moo/lib/gc.c

@@ -1082,6 +1082,7 @@ moo_oop_t moo_shallowcopy (moo_t* moo, moo_oop_t oop)
 
 		/* copy the payload */
 		MOO_MEMCPY (z + 1, oop + 1, get_payload_bytes(moo, oop));
+		MOO_OBJ_SET_FLAGS_RDONLY (z, 0); /* a copied object is not read-only */
 
 		return z;
 #else
@@ -1095,6 +1096,7 @@ moo_oop_t moo_shallowcopy (moo_t* moo, moo_oop_t oop)
 		moo_popvolat(moo);
 
 		MOO_MEMCPY (z, oop, total_bytes);
+		MOO_OBJ_SET_FLAGS_RDONLY (z, 0); /* a copied object is not read-only */
 		return z;
 #endif 
 	}

moo/lib/pf-basic.c

@@ -253,7 +253,6 @@ moo_pfrc_t moo_pf_shallow_copy (moo_t* moo, moo_mod_t* mod, moo_ooi_t nargs)
 	return MOO_PF_SUCCESS;
 }
 
-
 /* -------------------------------------------------------------------------------- 
  * BASIC ACCESS
  * -------------------------------------------------------------------------------- */