updates, more cautionary notes on R_alloc

git-svn-id: https://svn.r-project.org/R/trunk@63226 00db46b3-68df-0310-9c12-caf00c1e9a41
update

git-svn-id: https://svn.r-project.org/R/trunk@63228 00db46b3-68df-0310-9c12-caf00c1e9a41
update xz to 5.0.5

git-svn-id: https://svn.r-project.org/R/trunk@63230 00db46b3-68df-0310-9c12-caf00c1e9a41