identical() now looks at the S4 bit

git-svn-id: https://svn.r-project.org/R/trunk@66620 00db46b3-68df-0310-9c12-caf00c1e9a41
Moved Rtanpi declaration to arithmetic.h.


git-svn-id: https://svn.r-project.org/R/trunk@66621 00db46b3-68df-0310-9c12-caf00c1e9a41