adjusted some MPI send operations (switch to StgWord8)
Linux part of CpComm switch to StgWord8 data

internal send and receive methods switched to StgWord8,
(cpw_shm_send, cpw_shm_recv, cpw_self_recv).
changes mainly in removal of sizeof(long) from memcpy calls
inside the methods.

cpw_msg_t[ag] contains StgWord* data pointing to data area,
no changes required here.