Add support for new metadata directive `Uses:` or `Requires:`

[srcshelton]

At the moment, a schema-file may call a Stored Procedure... but we may have upgraded past this version.

• Check the logic to see whether current --substitute could also be made to apply to CALL() statements when schema-files are loaded;
• Add a Uses: (or similar) metadata directive to specify the (versioned, presumably) Stored Procedure(s) required to load the file contents.