Tidy: Remove redundant named anchors

[jhermann]

Named or link-less anchors around or in a header (H1…5) can result from copy-pasting HTML into a page. They tend to bleed into the surrounding text when using the "rich" editor of the latest releases (after saving, the new DOM is dirtied with the duplicates). This creates a visual problem, since the default CSS does not discriminate between normal links and named anchors.

Add some code that removes any Anchor nodes with the same name attribute, except the first one. Or put another way, replace any duplicate anchor node with its children, or morph it into a span.