- dune-istl is DuneIstl to CMAKE (e.g. during the find_package

  call). Mimic this in the variable names used in the package
  configuration files. (They were wrong anyway!)
- provide optional dependency to  create_doc_install. This is needed
  as add_latex_document with the safepdf option creates a target
  <basename>_safepdf for building <basename>.pdf. Without specifying
  <basename>_safepdf as the dependency, <basename>.pdf would be build
  in non-safe mode before install leading to errors with eps figures.

[[Imported from SVN: r1577]]