Make AbstractSession.getCachedInstance meet contract of method.

* Method should not return false but null.
* Various callers using method check whether return value != null and currently get
 false positives (since Boolean.FALSE != null).
GRAILS-3463 - added a relevant comment
MongoDB: ensure that to-manys inside embedded entities use reference mapping spec.

* Added test case checking both reference:false and reference:true cases
* Checked all places creating DBRefs - others are fine.
cleanup, whitespace, STS warnings
cleanup, updated to latest release plugin
Merge pull request #90 from tomwidmer/collection-unset-bug

Make AbstractSession.getCachedInstance meet contract of method.
Merge pull request #91 from tomwidmer/embedded-coll-dbrefs

MongoDB: ensure that to-manys inside embedded entities use reference map...
MongoDB optimistic locking updates implemented.

Version is now atomically updated using a 'compare and exchange' type
atomic operation, avoiding possible race conditions in a
multi-threaded or multi-process situation.

Note that this means at least an 'acknowledge' level of write concern is always
used for versioned entities.

Added a corresponding note to the docs.
Merge pull request #87 from tomwidmer/atomic-versioning

MongoDB optimistic locking updates implemented.
fix compile errors
neo4j: refactoring optional arg constructor
neo4j: removing explicit transaction manager configuration, relying on SpringConfigurer's defaults
Make sure AbstractPersistenceEvent.entityObject field is set.

It can be set from the entityAccess, and clients of the event
might want to access it without having to go via entityAccess.
Implement ValidationEvent firing.

Added full tests for persistence event listeners.
Merge pull request #93 from tomwidmer/validation-event

Validation event
Add bidirectional association support for embedded entities.

* Modify test cases to check inverse links work for one-to-many and one-to-one.
* Modify mapping strategy class to use same bidirectional code for embedded and non-embedded.
* Prevent infinite recursion saving embedded entities with bidirectional associations.
* Implement code to fix-up back-links when loading embedded entities.
Merge pull request #94 from tomwidmer/embedded-bidi

Add bidirectional association support for embedded entities.
changed to lowest possible dynamodb throughput values now that they lowered it on their end: set to 1
cosmetics in javadoc describing how to run locally
fixed failing AWS DynamoDB test