x11-wm/e16: update to 1.0.18

• Use AC_USE_SYSTEM_EXTENSIONS.
• Build .xz tarball too.
• Use RandR data to populate screens structure.
• Remove unused Mode.display.xinerama_active.
• Refactor some screen stuff.
• Refactorization in WarpFocus().
• Window list: Show windows on same head as pointer first.
• Drop incomplete HAVE_STDARG_H stuff.
• Fix warning with recent pango.
• Warning fixes for gcc 7.