this used to be a marker for places where x11 functionality was needed,
but this has been simplified with the removal of wayland-only in configure
and so it is no longer needed
this will mean all users upgrading from e18 to e19 get the new preview
pager. thoose wanting the older plain pager can switch ti pager_plain.
anyon using git will find pager16 remove (or if still installed not
updated) so switch back to pager from pager16. :)