x11-wm/xfce4-session:

• Update patch-scripts_xflock4 to add support for x11/i3lock
• Don't hard code /usr/local/bin in patch; change to %%LOCALBASE%%/bin

Approved by: sbruno (maintainer with XFCE hat), adamw (mentor)
Differential Revision: https://reviews.freebsd.org/D6884