allow setting names to NULL on call and dots objects

git-svn-id: https://svn.r-project.org/R/trunk@67159 00db46b3-68df-0310-9c12-caf00c1e9a41
consider DOTSXP when computing object.size

git-svn-id: https://svn.r-project.org/R/trunk@67160 00db46b3-68df-0310-9c12-caf00c1e9a41
dput(pairlist(x)) makes a call to pairlist(), not list()

git-svn-id: https://svn.r-project.org/R/trunk@67161 00db46b3-68df-0310-9c12-caf00c1e9a41
isPairList() returns TRUE for DOTSXP, as it does for other pairlist-derived types like NILSXP and LANGSXP

git-svn-id: https://svn.r-project.org/R/trunk@67162 00db46b3-68df-0310-9c12-caf00c1e9a41