add note on latin-9 vs latin9

git-svn-id: https://svn.r-project.org/R/trunk@62870 00db46b3-68df-0310-9c12-caf00c1e9a41
update zlib

git-svn-id: https://svn.r-project.org/R/trunk@62873 00db46b3-68df-0310-9c12-caf00c1e9a41
make FF registration checks optional

git-svn-id: https://svn.r-project.org/R/trunk@62875 00db46b3-68df-0310-9c12-caf00c1e9a41
avoid some false positives

git-svn-id: https://svn.r-project.org/R/trunk@62876 00db46b3-68df-0310-9c12-caf00c1e9a41
Check package Makevars files for overrides of variables to be used
for user/site customization of compilation.

git-svn-id: https://svn.r-project.org/R/trunk@62877 00db46b3-68df-0310-9c12-caf00c1e9a41