Fix PR#15970, tcltk getting messed up by redefinition of <-.

git-svn-id: https://svn.r-project.org/R/trunk@66571 00db46b3-68df-0310-9c12-caf00c1e9a41
as.list(<empty envir>) |--> list()

git-svn-id: https://svn.r-project.org/R/trunk@66572 00db46b3-68df-0310-9c12-caf00c1e9a41