Check whether current R session supports X11 or not.
Contrary to capabilities("X11")
which only checks for X11
support on startup [1], this function checks whether X11 is supported
when it is called. This is done by querying a temporary R session.
capabilitiesX11(reset=FALSE, ...)
Henrik Bengtsson
[1] R-devel thread 'capabilities("X11"): Force refresh from within R?
(... and minor documentation issue)' on 2015-05-06,
https://stat.ethz.ch/pipermail/r-devel/2015-May/071100.html