xvfb-run temp directory

[eddelbuettel]

When accepting it on CRAN (with some hesitation), Uwe wrote back

1. Looking into the xvfb-run-safe

# allow settings to be updated via environment
: "${xvfb_lockdir:=$HOME/.xvfb-locks}"
: "${xvfb_display_min:=99}"
: "${xvfb_display_max:=599}"

# assuming only one user will use this, let's put the locks in our own home directory
# avoids vulnerability to symlink attacks.
mkdir -p -- "$xvfb_lockdir" || exit

suggests this is against CRAN plicies, i.e. it creates files / dirs outside tempdir()?