[Rd] Shouldn't grDevices::quartz() give an error instead of a warning when not available?

[Henrik Bengtsson]

Compare:

> quartz(); cat("Should this have generated an error instead?\n")
Warning message:
In quartz() : Quartz device is not available on this platform
Should this have generated an error instead?

to:

> x11()
Error in .External2(C_X11, d$display, d$width, d$height, d$pointsize,  :
  unable to start device X11cairo
In addition: Warning message:
In x11() : unable to open connection to X11 display ''

Wouldn't it make sense that a failed call to quartz() would give an
error instead?

> sessionInfo()
R Under development (unstable) (2015-01-09 r67397)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
[1] C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

/Henrik