Improve messages.

git-svn-id: https://svn.r-project.org/R/trunk@63089 00db46b3-68df-0310-9c12-caf00c1e9a41
Texinfo markup.

git-svn-id: https://svn.r-project.org/R/trunk@63090 00db46b3-68df-0310-9c12-caf00c1e9a41