typo, mention interactive()

git-svn-id: https://svn.r-project.org/R/trunk@67138 00db46b3-68df-0310-9c12-caf00c1e9a41
mention --run-donttest

git-svn-id: https://svn.r-project.org/R/trunk@67140 00db46b3-68df-0310-9c12-caf00c1e9a41
suggest explanatory comment

git-svn-id: https://svn.r-project.org/R/trunk@67141 00db46b3-68df-0310-9c12-caf00c1e9a41