Made sure to clone when adding to used context.
Made sure to clone when adding to used context.

- Since used context is only updated using a clone of an entire
  context via _applyContext() (in the current code), this clone
  should be unnecessary, but it was added to ensure safer use
  of those functions that add to the used context.

digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch