Update JUnit tests to account for new anchoring location of
the delete message on the destruction occurrence shape.

Signed-off-by: Christian W. Damus <give.a.damus@gmail.com>

- Handle moving an execution to make it nested in another
- Handle moving an execution to make it nest another
- Ensure that the user cannot reshape execution specifications
  to effect partial nesting (incomplete overlap of extent)
- Indirectly fix eclipsesource#422 redundant nudging of nested executions

Signed-off-by: Christian W. Damus <give.a.damus@gmail.com>

…into 411-exec-nesting

Address the case identified in code review of a nesting
execution being resized leaving a formerly nested execution
hanging in space.

Includes update to the auto-fixture rule to support optional
(dynamic) fixtures to simplify again the specification of tests.

Signed-off-by: Christian W. Damus <give.a.damus@gmail.com>