Work around a bug in Cython with using my mpi4py

Author: Dag Sverre Seljebotn

python/libsharp/libsharp_mpi.pyx

@@ -1,10 +1,17 @@
-from mpi4py.MPI cimport Comm
+cdef extern from "mpi.h":
+    ctypedef void *MPI_Comm
+
 cdef extern from "Python.h":
     object PyLong_FromVoidPtr(void*)
 
+cdef extern:
+    ctypedef class mpi4py.MPI.Comm [object PyMPICommObject]:
+        cdef MPI_Comm ob_mpi
+        cdef unsigned flags
+
 # For compatibility with mpi4py <= 1.3.1
 # Newer versions could use the MPI._addressof function
-def _addressof(comm):
+def _addressof(Comm comm):
     cdef void *ptr = NULL
-    ptr = <void*>&(<Comm>comm).ob_mpi
+    ptr = <void*>&comm.ob_mpi
     return PyLong_FromVoidPtr(ptr)