[Rd] is.na(valid_date) too often true on SGI MIPS (PR#6814)

[aa056 at chebucto.ns.ca]

Full_Name: George N. White III
Version: 1.9.0
OS: Irix 6.5.21m
Submission from: (NULL) (142.176.61.212)


R-1.9.0 built using the SGI MIPSPro compilers

  Installation directory:    /usr/local

  C compiler:                c99 -OPT:IEEE_NaN_inf=ON -mips4 -n32 -O3
-OPT:Olimit_opt=on
  C++ compiler:              CC -OPT:IEEE_NaN_inf=ON -mips4 -n32 -O3
-OPT:Olimit_opt=on -LANG:std
  Fortran compiler:          f90 -OPT:IEEE_NaN_inf=ON -mips4 -n32 -O3
-OPT:Olimit_opt=on

  Interfaces supported:      X11, gnome, tcltk
  External libraries:        readline, BLAS(generic), LAPACK(generic)
  Additional capabilities:   PNG, JPEG
  Options enabled:           shared library, R profiling

  Recommended packages:      yes

"make check" fails in 2 places due to is.na(..) returning TRUE for valid dates:

> d<-strptime("1910/1/1", "%Y/%m/%d")
> is.na(d)
[1] TRUE
> d
[1] "1910-01-01"

> d<-strptime("1970/1/1", "%Y/%m/%d")
> is.na(d)
[1] FALSE
> d
[1] "1970-01-01"

Incidentally:
> NA+NaN;NaN+NA
[1] NA
[1] NaN