new assertCondition() from John Chambers

git-svn-id: https://svn.r-project.org/R/trunk@63062 00db46b3-68df-0310-9c12-caf00c1e9a41
parallel: avoid broken pipes by re-routing to /dev/null instead of closing stdout

git-svn-id: https://svn.r-project.org/R/trunk@63063 00db46b3-68df-0310-9c12-caf00c1e9a41
Raise an error on log(base=4), round(digits=4), etc. (PR#15361)

git-svn-id: https://svn.r-project.org/R/trunk@63065 00db46b3-68df-0310-9c12-caf00c1e9a41