Non-globally-unique anchor links get confused

[mnelson4]

If two posts have a block with ID "linkhere", and a link to it, and they're both included in the same project, links to them will get confused.
Anchor links should prioritize linking to anchors in their own post; but if none exists, it's OK to link to an anchor in a different post.
The best algorithm for this eludes me at the moment...