allow mca_pml_comm_t to be redefined on a per-pml basis

This commit was SVN r375.

src/mpi/communicator/communicator.h

@@ -31,7 +31,7 @@ struct lam_communicator_t {
     MPI_Errhandler c_error_handler;
 
     /* Hooks for PML to hang things */
-    void* c_pml_comm;
+    struct mca_pml_comm_t* c_pml_comm;
 
     /* Hooks for collectives to hang things */