Re: mf:requires

ACTION: AndyS: Invent and document an alternative to mf:requires for things 
that are noteable but not extensions in the test suite
ACTION: AndyS: Update manifest for mf:requires
ACTION: AndyS: Update vocabulary files and README for test

I've updated:

tests/README.html
tests/test-manifest.n3
tests/data-r2/open-world/manifest.ttl

The invented property is "mf:notable"

	Andy

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