more consistent handling of attributes by unary operators

git-svn-id: https://svn.r-project.org/R/trunk@63333 00db46b3-68df-0310-9c12-caf00c1e9a41
fix for PR#15231

git-svn-id: https://svn.r-project.org/R/trunk@63335 00db46b3-68df-0310-9c12-caf00c1e9a41