Fix bug in trans_field, un-XFAIL two more tests.

src/Makefile

@@ -449,6 +449,7 @@ TEST_XFAILS_RUSTC := $(filter-out \
                         arith-0.rs \
                         arith-1.rs \
                         arith-2.rs \
+                        auto-instantiate.rs \
                         autoderef-full-lval.rs \
                         bind-exterior.rs \
                         bind-interior.rs \
@@ -479,6 +480,7 @@ TEST_XFAILS_RUSTC := $(filter-out \
                         generic-exterior-box.rs \
                         generic-drop-glue.rs \
                         generic-obj.rs \
+                        generic-obj-with-derived-type.rs \
                         generic-tup.rs \
                         generic-type.rs \
                         generic-type-synonym.rs \

src/comp/middle/trans.rs

@@ -2376,10 +2376,8 @@ fn trans_path(@block_ctxt cx, &ast.path p, &option.t[ast.def] dopt,
 
 fn trans_field(@block_ctxt cx, &ast.span sp, @ast.expr base,
                &ast.ident field, &ast.ann ann) -> lval_result {
-    auto lv = trans_lval(cx, base);
-    auto r = lv.res;
+    auto r = trans_expr(cx, base);
     r = autoderef(r.bcx, r.val, ty.expr_ty(base));
-    check (lv.is_mem);
     auto t = ty.expr_ty(base);
     alt (t.struct) {
         case (ty.ty_tup(?fields)) {