issue #400 add warning message with instructions when RandomTree can fails
issue #400 add warning message with instructions when RandomTree can fails

Anaphory/beast2,CompEvol/beast2,CompEvol/beast2,CompEvol/beast2,Anaphory/beast2,tgvaughan/beast2,Anaphory/beast2,tgvaughan/beast2,CompEvol/beast2,tgvaughan/beast2,Anaphory/beast2,tgvaughan/beast2