x11/xscreensaver: Update to 6.06

Changelog:

• New hack, hextrail.
• marbling works again.
• Adjusted some of the very old hacks, which were written when pixels were larger, to be more visible on today's higher rez displays.
• X11: More robust desktop image grabbing.
• X11: Various improvements to xscreensaver-settings.
• X11: Silence new new Perl warnings from xscreensaver-getimage-file.

Approved by: x11 (manu, maintainer), tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D37744