Indexing: clear versionMap on refresh (not flush) to reduce heap usage

The versionMap holds all versions (keyed by _uid) for recently indexed
documents.  Previously we only cleared it during flush, which can be
infrequent if the translog flush thresholds are high, and can cause
excessive heap usage especially for small documents.

Now we clear it during refresh which is usually more frequent
(e.g. once per second by default).

Closes #6379
Add Javadoc
[DOCS] Add special attributes for indices allocation filtering
get -Dtests.verbose passing through Maven
add versioning test
Core: switch to the new ConcurrentHashMap implementation coming in Java 8

The new implementation has lower RAM overhead and better concurrency
in some cases.

Closes #6400
Scripts: exposed _uid, _id and _type fields as stored fields (_fields notation)

The _uid field wasn't available in a script despite it's always stored. Made it available and made available also _id and _type fields that are deducted from it.

Closes #6406
revert CHMV8 for now (it doesn't compile under Java8)
[DOCS] Added Javadocs to ESLogger and ESLoggerFactory
[DOCS] Replace facets example with aggregations in warmers docs
[DOCS] Clean up Java-API docs

Fixed some wording and subject/verb agreement while reading through the Java API documentation.
[DOCS] Fixed typo in object-type.asciidoc
Core: switch to the new ConcurrentHashMap implementation coming in Java 8

The new implementation has lower RAM overhead and better concurrency
in some cases.

Closes #6400
[DOCS] Fixed typos in aggregations.asciidoc

Fix plural/singular forms.
[DOCS] fixed typo in date-format.asciidoc
[DOCS] Fixed the fuzzy query docs with correct default value max_expansion option
[DOCS] Fixed typo in put-mapping docs

split backwardscompatibility to backwards compatibility
make this new test a bit less stressful for nightly; catch FlushNotAllowedEngineException
[DOCS] Reworded note about shorthand suggest syntax

The existing Note about the shorthand suggest syntax was poorly worded and confusing. Please check whether the way I've phrased it now is still correct as to what the shorthand form actually does and doesn't do: the original wording did not provide me enough information to be sure.
Thanks!
Compilation: don't warn about using Sun proprietary APIs

E.g. we use Unsafe in quite a few places and this generates lots of
warnings, which we now suppress using the undocumented
-XDignore.symbol.file command-line option to javac.

Closes #6423