A small C program that retrieves all information about DPI (dots per inch)
of the available displays in X11.
Information from both the core protocol and the XRANDR extension is presented.
Xinerama information (which lacks physical dimensions,
and is thus not directly useful to determine output DPI) is also presented.
If an XSETTINGS daemon is found, the reported (scaled and raw) Xft/DPI value is
presented.
