Add a note about ugni memory registration and concurrency with slurm.
Merge pull request #587 from gbtitus/doc-slurm-ugni-mem-registration-issue

Add a note about ugni memory registration and concurrency with slurm.

Reviewed by Thomas.
Fix nondeterministic output from walkdir() by requesting sorted output
Merge pull request #590 from bradcray/fix-filerator-regression

Fix nondeterministic output from walkdir() by requesting sorted output

[trivial, not reviewed]

I forgot to request sorted output in my new test yesterday, which
resulted in nondeterministic behavior across file systems/machines.
This broken in one configuration last night (and could break in others
over time).