fix to make pureNullUnitValue() recursive

git-svn-id: https://svn.r-project.org/R/trunk@65845 00db46b3-68df-0310-9c12-caf00c1e9a41
workaround for the non-reproducible PR#15815

git-svn-id: https://svn.r-project.org/R/trunk@65846 00db46b3-68df-0310-9c12-caf00c1e9a41
document workaround

git-svn-id: https://svn.r-project.org/R/trunk@65847 00db46b3-68df-0310-9c12-caf00c1e9a41
add EOL

git-svn-id: https://svn.r-project.org/R/trunk@65851 00db46b3-68df-0310-9c12-caf00c1e9a41
Replaced case 0: with case CE_NATIVE: for consistency.


git-svn-id: https://svn.r-project.org/R/trunk@65852 00db46b3-68df-0310-9c12-caf00c1e9a41
add some C/C++ portability notes

git-svn-id: https://svn.r-project.org/R/trunk@65854 00db46b3-68df-0310-9c12-caf00c1e9a41