MODE-1971 Fixed the copy operation so that connectors are involved in the id-creation step. Also, implemented the rename operation (via copy) for the FileSystem connector.
MODE-1968 Improved/simplified logging of persisted changes

When a session is saved, the WritableSessionCache now outputs
more details of the changes to the 'org.modeshape.jcr.txn' logging
context under TRACE logging. This logging context does not match
the normal conventions, but it makes it really easy to turn on
TRACE logging on this context and see all the save- and transaction-
related information.
MODE-1968 Corrected test case
MODE-1961 Fixed the processing of mixins when nodes are imported from an
XML file using IMPORT_UUID_COLLISION_REMOVE_EXISTING, multiple times. The problem was
caused by the fact that the same NodeKey is reused, causing in effect the
old persisted node(s) to be seen together with new nodes (which are
supposed to be created by the import). Thefore, mixins would not be set on
the new nodes because they appeared as "already existing".