Fixes #4239: Move r30642 to v1.7 branch (purge stale session dirs at startup)

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r30642 [[BR]]
In case there are stale session directories around, do a purge of the relevant session directory tree when an orted, HNP, or singleton start. This won't help in the case of direct-launched apps, but it's the best we can do.

cmr=v1.7.5:reviewer=jsquyres:subject=purge stale session dirs at startup
Minor cleanups
Fixes #4053: Move r30123, 30288, 30476, 30626, 30652, r30668 to v1.7 branch (vader fixes)

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r30123 [[BR]]
btl/vader: add support for traditional shared memory.

This commit adds support for placing the send memory segment in a
traditional shared memory segment when XPMEM is not available. The
current default is to reserve 4MB for shared memory on each process.
The latest benchmarks show vader performing better than sm on both
Intel and AMD CPUs.

For large messages vader will now use CMA if it is available (and
XPMEM is not).

cmr=v1.7.5:reviewer=jsquyres

r30284 [[BR]]
vader: don't OBJ_RELEASE endpoint rcaches.

cmr=v1.7.4:reviewer=rhc

r30288 [[BR]]
vader: ensure fast box data is aligned on 4-byte boundaries

This commit fixes a bus error on Solaris/Sparc.

Closes #4111

cmr=v1.7.5:ticket=#4053

r30476 [[BR]]
btl/vader: add support for SGI's implementation of xpmem and add support
for 32-bit architectures.

This commit also modifies _OMPI_CHECK_HEADER to use AC_CHECK_HEADERS instead
of AC_CHECK_HEADER. This allows components to check for multiple headers
instead of just one. The new semantics of the header check in OMPI_CHECK_PACKAGE
are to return success if at least one of the specified headers exists. The new
semantics will not break current usage.

cmr=v1.7.5:ticket=#4053

r30626 [[BR]]
btl/vader: fix 32-bit support

cmr=v1.7.5:ticket=#4053

r30652 [[BR]]
vader: fix typos in r30626

cmr=v1.7.5:ticket=#4053

r30668 [[BR]]
vader: don't finalize an endpoint that is already finalized

Fixes #4252

cmr=v1.7.5:ticket=#4053
Fixes #4242: Move r30645 to v1.7 branch (add a plm component for local-only operation)

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r30645 [[BR]]
Add a plm component for local-only operation that doesn't require rsh/ssh to be installed. Requested by Fedora packagers for testing purposes.

cmr=v1.7.5:reviewer=jsquyres:subject=Add a plm component for local-only operation