Incorrect PMC linkouts

[cbizon]

This is an edge from TMKP:

The publications are PMC (pubmed central) but the linkouts are PMID (but with the same number as the PMC).

These are different naming schemes, so the papers that are returned are the wrong ones. i.e. the edges says PMC:123, but we are linking to PMID:123, which is a completely different and incorrect paper.