We documented that huffman_key and huffman_value took "none" as an
argument, but they didn't.

Worse, if key was set but not value, we'd set value anyway, free of
charge, and if value was set but not key, we'd fail. I doubt this
is a problem (it's pretty surprising if anyone would set key but not
also set value).

Use __wt_config_gets_none() to support the "none" setting, re-work
the logic to ignore keys or values that are zero-length.

Reference #1417.
We document block_compressor supports a value of "none", but didn't
change the config call to the new __wt_config_gets_none version.
Reference #1417.
Make the huffman_key, huffman_value default values "none", rather than
"empty string", for clarity.
Remove the code that checks for some shared-cache features being
specified but not all of them, otherwise users can't turn off an
application's shared cache implementation by just setting the name
to "none". Reference #1417.
The shared_cache.name configuration string supports "none", document
that fact, and change the default from the empty string to "none" for
clarity. Reference #1417.
Don't set the LSM tree collator to "none" if that's what was specified.
When creating a data-source, allow for a collator set to the empty string
or to "none", we document that now.
Merge branch 'develop' into none-config-2
Allow extractors set to an empty string or "none".
Change the extractor configuration default from the empty string to
"none" for clarity.
Support extractors configured as "none".
Typo, __wt_config_getones_none should call __wt_config_getones,
not itself.
Return an error if a shared cache configuration is set, but
not enabled.

Check for a configuration via shared_cache=(size=).

Refs #1487
Use none comparison when checking for invalid collator usage.
Merge pull request #1486 from wiredtiger/none-config-2

Some more configuration changes with respect to the "none" value.