Make addAnchor more robust

[Mitar]

I recommend that addAnchor JavaScript call is more robust like:

$("#content").find("h1,h2,h3,h4,h5,h6").filter("[id]").addAnchor("Link to this section");

In this way those headings without id would not be processed. Currently they are but there is no use of such anchor link which points to nowhere.

Such headings without ids (or where ids are not appropriate because headings are used in different context) are possible as a result of macros, for example.

[Christian Boos]

Well, addAnchor()​ itself takes care of this.

[Mitar]

True. This was discrepancy because I have manually upgraded jQuery but had addAnchor() for older version.