Ensure semantic checking can handle large numbers of clauses
Some formatting and streamlining for the SubGraphExporter

Specifically being more defensive against a future where indexes and constraints
might have more than one property key.
Merge pull request #1787 from cleishm/semantic_check_optimization

Ensure semantic checking can handle large numbers of clauses
Try making the StartupTimeoutFunctionalTest less prone to spurious failure.
Merge pull request #1784 from chrisvest/subgraph-exporter-formatting-and-cleanup

Some formatting and streamlining for the SubGraphExporter