Improve comments relating to "ghost buffers"

Improve comments relating to "ghost buffers"

* Correct and extend various parameter comments, esp. for Doxygen
* Make sure default parameter values in a function definition are
properly commented in the function declaration as well
* Add either `/*virtual base*/` or `/*virtual override*/` comments to
various "ghost buffer " related procedure declarations.
* Eliminate (using `#if 0` and `#endif`) the procedures
`InternalInsertGhostLine()` and `InsertGhostLine()`