Generate N-Quads for IMS linksets

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Sometimes it can be beneficial to use the IMS linksets directly from SPARQL. Potential commercial users of Open PHACTS data has asked for this functionality.

However there is no consistent way to preprocess or load the current linksets while also retaining the link between the VoID and the loaded linkset - particularly as the use of @base is not consistent across the VoIDs.

This bug proposes a preprocessing step which can make nquads files of the loaded linksets, typically one graph per void and per linkset. This dataset can then be included in the Virtuoso cache.

Note that this is different from auto-generating transitive linksets from IMS or equivalent - these linksets will just replicate the original linksets loaded into IMS, split into graphs.