Move parallel support imports to .pxi so shims get correct type

We also need to explicitly cast the comm/info arguments to the correct type

include/netCDF4.pxi

@@ -384,6 +384,8 @@ cdef extern from "numpy/arrayobject.h":
     void import_array()
 
 
+include "parallel_support_imports.pxi"
+
 # Compatibility shims
 cdef extern from "netcdf-compat.h":
     int nc_rename_grp(int grpid, char *name) nogil
@@ -424,8 +426,6 @@ cdef extern from "netcdf-compat.h":
                          unsigned* addshufflep) nogil
 
     # Parallel shims
-    ctypedef int MPI_Comm
-    ctypedef int MPI_Info
     int nc_create_par(char *path, int cmode, MPI_Comm comm, MPI_Info info, int *ncidp) nogil
     int nc_open_par(char *path, int mode, MPI_Comm comm, MPI_Info info, int *ncidp) nogil
     int nc_var_par_access(int ncid, int varid, int par_access) nogil

include/no_parallel_support_imports.pxi.in

@@ -1,8 +1,10 @@
 # Stubs for when parallel support is not enabled
 
+ctypedef int MPI_Comm
+ctypedef int MPI_Info
 ctypedef int Comm
 ctypedef int Info
-cdef Comm MPI_COMM_WORLD
-cdef Info MPI_INFO_NULL
+cdef MPI_Comm MPI_COMM_WORLD
+cdef MPI_Info MPI_INFO_NULL
 MPI_COMM_WORLD = 0
 MPI_INFO_NULL = 0

src/netCDF4/_netCDF4.pyx

@@ -1244,7 +1244,6 @@ from numpy import ma
 from libc.string cimport memcpy, memset
 from libc.stdlib cimport malloc, free
 numpy.import_array()
-include "parallel_support_imports.pxi"
 include "membuf.pyx"
 include "netCDF4.pxi"
 
@@ -2265,11 +2264,11 @@ strings.
                 msg='parallel mode only works with the following formats: ' + ' '.join(parallel_formats)
                 raise ValueError(msg)
             if comm is not None:
-                mpicomm = comm.ob_mpi
+                mpicomm = (<Comm?>comm).ob_mpi
             else:
                 mpicomm = MPI_COMM_WORLD
             if info is not None:
-                mpiinfo = info.ob_mpi
+                mpiinfo = (<Info?>info).ob_mpi
             else:
                 mpiinfo = MPI_INFO_NULL
             parmode = NC_MPIIO | _cmode_dict[format]