BUG: accept Atom occupancy of np.int64 type

Problem: boost python has no implicit conversion numpy.int64 --> double.
Solution: convert value to float.

Author: pavoljuhas

src/diffpy/srreal/structureconverters.py

@@ -142,7 +142,7 @@ def _fetchDiffPyStructureData(adpt, stru):
     aa = AdapterAtom()
     for a0 in stru:
         aa.atomtype = a0.element
-        aa.occupancy = a0.occupancy
+        aa.occupancy = float(a0.occupancy)
         aa.anisotropy = a0.anisotropy
         # copy fractional coordinates
         aa.xyz_cartn = a0.xyz

src/diffpy/srreal/tests/teststructureadapter.py

@@ -60,7 +60,6 @@ def test_createStructureAdapterTypes(self):
         self.assertTrue(type(adpt3) is DiffPyStructureAtomicAdapter)
         return
 
-    @unittest.expectedFailure
     def test_createStructureAdapter_int64_occupancy(self):
         """Check Structure conversion when occupany is of numpy.int64 type.
         """