Fix display of primitives, etc. in symbol index

[pkgw]

In the index, primitives currently show up like:

exttt {\doublehyphendemerits} primitive

This is clearly because something is rendering them with something like \texttt{\\doublehyphendemerits} primitive, and at some point in the process we're not handling it correctly. We should fix that! There are also a variety of other names that aren't showing up nicely.