Fix type alias initialization

Type alias for alias classes with members didn't work properly: space
was only allocated for sizeof(type), but if we want to be able to put a
type_alias instance there, we need sizeof(type_alias), but
sizeof(type_alias) > sizeof(type) whenever type_alias has members.
diff --git a/tests/test_issues.py b/tests/test_issues.py
index 86bd6a5..2af6f1c 100644
--- a/tests/test_issues.py
+++ b/tests/test_issues.py
@@ -169,15 +169,15 @@
 
 def test_override_ref():
     from pybind11_tests.issues import OverrideTest
-    o = OverrideTest(42)
+    o = OverrideTest("asdf")
 
     # Not allowed (see associated .cpp comment)
-    #i = o.int_ref()
-    #assert o.int_ref() == 42
-    assert o.int_value() == 42
+    #i = o.str_ref()
+    #assert o.str_ref() == "asdf"
+    assert o.str_value() == "asdf"
 
-    assert o.A_value().value == 99
+    assert o.A_value().value == "hi"
     a = o.A_ref()
-    assert a.value == 99
-    a.value = 7
-    assert a.value == 7
+    assert a.value == "hi"
+    a.value = "bye"
+    assert a.value == "bye"