BUG-648: Improve performance by reusing old data nodes

This patchset gives yang-data-api the chance to optimize copy
operations we execute when creating a new generation.

Change-Id: Ib23a87e116a0a04f7fd4f2b709d7239e213ea744
Signed-off-by: Robert Varga <rovarga@cisco.com>
Bug 981: Fixed accidental shaddowing of data in Data Change Event.

Not all Normalized DOM InstanceIdentifier has their counterpart
in Binding-Aware representation. Added explicit check to
detect mixin instance-identifiers which could lead to
incorrect deserialization into maps and shadowing parent data.

Change-Id: I66166f50c636ce0dfcd962efac7fc488da622336
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>