Announce: http://www.xfce.org/about/news/?post=1425081600

Global changes:
- Switch to USES= xfce (D677)
- Reorganize options helper
- Fix USES= gettext-* when NLS option is not set [1], [2]
- Add LICENSE (when missing)

Update:
- to 4.12 (core components)
- audio/xfce4-mpc-plugin to 0.4.5
- deskutils/xfce4-tumbler to 0.1.31
- deskutils/xfce4-xkb-plugin to 0.7.1
- editors/mousepad to 0.4.0
- graphics/ristretto to 0.8.0
- multimedia/xfce4-parole to 0.8.0
- sysutils/garcon to 0.4.0
- sysutils/xfce4-diskperf-plugin to 2.5.5 [3]
- sysutils/xfce4-fsguard-plugin to 1.0.2
- sysutils/xfce4-power-manager to 1.4.3
- sysutils/xfce4-wavelan-plugin to 0.5.12
- x11/libexo to 0.10.3
- x11-fm/thunar to 1.6.6
- x11-themes/gtk-xfce-engine to 3.2.0

PR:		196003 [1], 197251 [2], 198132
Differential Revision:	https://reviews.freebsd.org/D677
Submitted by:	Kamil Szczesny [1], amdmi3@ [2], myself
Exp-run by:	antoine@
Approved by:	danilo@ (maintainer) [3]
Tested by:	Ivan <enitarzi@gmail.com>