Add sections on locking and remote shares to unix/windows (rebased onto develop)

[joshmoore]

This is the same as gh-227 but rebased onto develop.

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This comes after several reports on the mailing lists of NFS and CIFS installs
failing.

Questions

• Is the section obvious enough? Do we need a red blinking banner?
• Are all of the terms well-enough understood? Do we need links?
• Are there any tests that can be performed to check locking?
• Should we also add a section on latency?

/cc @chris-allan

[bpindelski]

Looks good to merge and provides proper explanation.

[joshmoore]

Thanks, @bpindelski