Fixes #4076: Move r30183 to v1.7 branch (fix use of non-portable makefile macro)

NOTE: some hand cleanup as the oshmem stuff isn't in the 1.7 branch yet

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r30183 [[BR]]
Use the portable "$?" macro to build examples.

Thanks to Paul Hargrove for reporting the issue.

cmr=v1.7.4:reviewer=rhc:subject=Fix use of non-portable Makefile macro

r30184 [[BR]]
Only check for the MPI / OSHMEM	bindings if we can find	ompi_info /
oshmem_info in the path.

Refs #4076
Fixes #4075: Move r30182 to v1.7 branch (ensure slurm properly dies on abnormal termination)

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r30182 [[BR]]
Ensure slurm properly dies on abnormal termination

cmr=v1.7.4:reviewer=jsquyres:subject=Ensure slurm properly dies on abnormal termination
Fixes #4072: Move r30178 to v1.7 branch (Add missing MCA variable enumerator)

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r30178 [[BR]]
Add missing MCA variable enumerator sentinel.

cmr=v1.7.4:reviewer=rhc
Fixes #4071: Move r30176 to v1.7 branch (mxm: fixes for compilation warnings.)

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r30176 [[BR]]
mxm: fixes for compilation warnings.
    
removed set but not used variables and a variable that is unused.

reviewed by miked
cmr=v1.7.4:reviewer=ompi-rm1.7
Fixes #4069: Move r30174 to v1.7 branch (Fix typo in udreg mpool)

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r30174 [[BR]]
Fix typo in udreg mpool that could cause us to try to use an invalid
registration. This was causing transaction errors on Aries systems.

cmr=v1.7.4:reviewer=rhc