Fixes #4489: Move r31308, 31348, r31351 to v1.8 branch

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r31308 [[BR]]
Not sure when this got messed up, but correct the stdout/stderr redirection on the srun command so we don't get all those slurm warnings

cmr=v1.8.1:reviewer=dgoodell:subject=silence srun warning output


r31348 [[BR]]
Okay, silence the anality by simplifying the already irrelevant code, thus allowing us to turn our attention to things that actually matter

Refs #4489


r31351 [[BR]]
plm/slurm: tweak /dev/null usage (#4489)

See the ticket for more details.

cmr=v1.8.1:reviewer=rhc:ticket=4489
Fixes #4498: Move r31333 to v1.8 branch (Fix the sequential mapper -)

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r31333 [[BR]]
Fix the sequential mapper - it was out-of-sync with the hostfile changes, and we missed the "seq" policy when parsing the --map-by option. Thanks to Bill Chen for reporting it

cmr=v1.8.1:reviewer=jsquyres
Fixes #4500: Move r31346, r31350 to v1.8 branch (zsh/completion: declare ret as a)

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r31346 [[BR]]
zsh/completion: fix full completion and add support for subcommand
completion

_normal forces completion to be done on the subcommand. This gives us two
things:

 - Completion of an executable for the first command argument

 - Completion of options for that executable if any exist. If not it
   will use normal completion rules (_files).

cmr=v1.8.1:reviewer=jsquyres

r31350 [[BR]]
zsh/completion: declare ret as a local variable and call the catch-all
completion from _arguments instead of treating it as a state

cmr=v1.8.1:ticket=#4500