fixes in datatypes

- Enum.__call__(self, value) should raise BadValueError when
  value is not hashable
- added TextType.copy (DataType.copy will not work here)

Change-Id: I6c460991fa1e6595a939fb0814f490d2188c97b4
Reviewed-on: https://forge.frm2.tum.de/review/21015
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_datatypes.py

@@ -174,7 +174,7 @@ def test_EnumType():
         dt(-9)
     with pytest.raises(ValueError):
         dt(u'XX')
-    with pytest.raises(TypeError):
+    with pytest.raises(ValueError):
         dt([19, u'X'])
 
     assert dt(u'a') == 3