Swiss billionaire gets 18 years jail for Italian asbestos deaths
* Negligence led to more than 2,000 asbestos-linked deaths
* Activists say will set precedent in work safety cases
* Schmidheiny tried in absentia, will appeal
MILAN, June 3 (Reuters) - A billionaire Swiss industrialist convicted for his part in Italy's biggest asbestos scandal had his jail sentence lengthened to 18 years on Monday, in a ruling campaigners said would set a precedent for work-safety lawsuits.