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There are quite a few places where the request cleanup is done via:

MPIU_Object_set_ref(req, 0);
MPIDI_CH3_Request_destroy(req);

when it should be:

MPID_Request_release(req);

This makes the handling more uniform so requests are cleaned up by releasing
references rather than hitting them with the destroy hammer.

Fixes #1664
Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>