Welcome XFCE 4.16 to the FreeBSD ports tree!

Upstream announce: https://xfce.org/about/news/?post=1608595200

This XFCE release dropped support for GTK2 plugins and also dropped
GTK2 from all components.

WARNING: please check UPDATING before upgrading your packages. In
case of problems also read the libexo pkg-message.

Due to this some panel plugins and libraries will be removed since
they cannot compile anymore:

- print/xfce4-print
- x11/xfce4-quicklauncher-plugin
- x11/xfce4-wmdock-plugin
- x11-toolkits/libxfce4gui

These further components also fail to build or work and are being
marked BROKEN, deprecated and marked for removal:

- science/xfce4-equake-plugin
- x11/xfce4-embed-plugin
- deskutils/orage
- deskutils/xfce4-volumed [1]

deskutils/xfce4-notes-plugin will be also marked BROKEN, but there
is active development in it's upstream repository and a fixed release
is expected soon.

deskutils/xfce4-generic-slider will also be marked broken, since
it fails to compile. [2]

Thanks also to riggs, Olivier Duchateau <duchateau.olivier@gmail.com>
and the people in Approved and Reviewed lines below for help and
contributions.

Reviewed by:		woodsb02
Approved by:		sergey.dyatko@gmail.com (maintainer) [1],
			ehaupt [2]
Differential Revision:	https://reviews.freebsd.org/D27846