Fixes #4135: Move r30324 to v1.7 branch (fix a problem when opening a file with mode_excl)

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r30324 [[BR]]
fix the problem identified by a user on the mailing list with MPI_MODE_EXCL

cmr=v1.7.4:reviewer=vvenkatesan:subject=fix a problem when opening a file with MODE_EXCL
Fixes #4132: Move r30320 to v1.7 branch (The portable_platform file moved to)

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r30320 [[BR]]
The portable_platform file moved to opal at some point, but this .m4 didn't get updated to match.

Thanks to Paul Hargrove for spotting it and providing a patch!

cmr=v1.7.4:reviewer=jsquyres
Fixes #4153: Fix MX MTL module finalize in v1.7

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r27343 [[BR]]

Custom patch from
http://www.open-mpi.org/community/lists/users/2012/09/20202.php;
essentially reverting r26698 (from the trunk).