Suppress more messages when checking data for non-ASCII characters.

git-svn-id: https://svn.r-project.org/R/trunk@66542 00db46b3-68df-0310-9c12-caf00c1e9a41
Fix PR#15957, removeSource bug.

git-svn-id: https://svn.r-project.org/R/trunk@66543 00db46b3-68df-0310-9c12-caf00c1e9a41
back-merged item from 3-1-branch

git-svn-id: https://svn.r-project.org/R/trunk@66545 00db46b3-68df-0310-9c12-caf00c1e9a41