clarifications

git-svn-id: https://svn.r-project.org/R/trunk@62953 00db46b3-68df-0310-9c12-caf00c1e9a41
efficiency: s / try() / tryCatch() /     and  if(.) . else . instead of  ifelse()


git-svn-id: https://svn.r-project.org/R/trunk@62955 00db46b3-68df-0310-9c12-caf00c1e9a41
update

git-svn-id: https://svn.r-project.org/R/trunk@62956 00db46b3-68df-0310-9c12-caf00c1e9a41