MODE-2283 Corrected behavior when removing and then replacing strong reference props

When a reference value is changed, the `SessionNode` methods attempt to look for the
special case where the new (transient) reference value matches that of the
persisted value. IOW, given this code that sets up an initial persisted state:

```
Node referenceableNode = session.getRootNode().addNode("referenceable");
referenceableNode.addMixin(JcrMixLexicon.REFERENCEABLE.toString());

Node node1 = session.getRootNode().addNode("node1");
node1.setProperty("prop1", session.getValueFactory().createValue(referenceableNode, false));
session.save();
```

making the following changes transiently in the session:

```
node1.setProperty("prop1", session.getValueFactory().createValue(referenceableNode, false));
```

sets the property to the exact same value as persisted. `SessionNode` discovers this case
and that this operation makes no net changes to the persisted content, so it alters the
session's state to reflect this no-net-change.

Notice that the reported scenario is *close* to this, but it first removes the
property before resetting it back to the same value; this is a special case that
the `SessionNode` logic did not properly handle.

This PR corrects this behavior and adds a test case that replicated the problem before
the fix is applied, and verifies the fix works.

Conflicts:
	modeshape-jcr/src/main/java/org/modeshape/jcr/cache/document/SessionNode.java
Merge pull request #1224 from rhauch/mode-2283

MODE-2283 Corrected behavior when removing and then replacing strong reference props