Fixes #3740: Move r29095 to v1.7 branch (don't call OMPI_REQUEST_INIT in req)

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r29095 [[BR]]
don't call OMPI_REQUEST_INIT in req constructor

Calling OMPI_REQUEST_INIT puts the request into an _INACTIVE state
instead of an _INVALID state, which we don't want if it's been
simply been constructed, e.g., in a free_list.  Without this change a
future change to call destructors at free list destruction time will
result in request dtor state assertion failures.

Reviewed-by: bosilca

cmr=v1.7.4:reviewer=bosilca
Fixes #3741: Move r29096 to v1.7 branch (call element destructors in ompi_free_list_destruct)

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r29096 [[BR]]
call element destructors in ompi_free_list_destruct

The free list code called the constructor for each object it
slab allocated in ompi_free_list_grow.  This permits free list-managed
elements to safely allocate/deallocate resources in their
constructors/destructors without leaking.

It's probably best to let this soak on the trunk a little while before
moving it over to v1.7.

Reviewed-by: bosilca

cmr=v1.7.4:reviewer=bosilca
Fixes #3742: Move r29097 to v1.7 branch (usnic: stomp format specifier warnings)

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r29097 [[BR]]
usnic: stomp format specifier warnings

The usnic BTL now builds cleanly under `--enable-picky` when `MSGDEBUG1`
is set.

Reviewed-by: jsquyres

cmr=v1.7.4:reviewer=jsquyres
Fixes #3756: Move r29127 to v1.7 branch (usnic: properly destroy embedded small)

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r29127 [[BR]]
usnic: properly destroy embedded small send frag

Without this, an `--enable-debug` build would hit an assertion in the
list code when run under valgrind with `--malloc-fill=0xff` or any other
case where malloc returned non-zeroed buffers.

Also allow the normal OBJ_ machinery to handle the constructor
invocation ordering for us instead of doing it by hand (which could have
led to future bugs).

Reviewed-by: jsquyres@cisco.com

cmr=v1.7.4

Depends on trunk functionality in r29095 and r29096.  Refs #3740,#3741.