add a long needed ess-boolean-command

git-svn-id: https://svn.r-project.org/ESS/trunk@5559 0bbaf3bd-34e0-0310-bf65-c717079852d4
add startup checks and message to ess-developer

git-svn-id: https://svn.r-project.org/ESS/trunk@5560 0bbaf3bd-34e0-0310-bf65-c717079852d4