Update rxvt-unicode to 5.8. Patches provided by Leonard Schmidt

Update rxvt-unicode to 5.8.  Patches provided by Leonard Schmidt
(maintainer) in PR pkg/31930.

Changes:
	- INCOMPATIBLE CHANGE: many configure options are now on by default.
          If you want the old behaviour, try:
          configure --disable-everything <your enable options>
        - INCOMPATIBLE CHANGE: -fade changed its meaning to comply with
          the documentation and common sense: when upgrading, replace your
          percentage by 100-percentage.
        - integrated "fade to specific colour" patch by Martin Parm.
        - slow down the internal visual bell (delay by 20ms) and update
          the terminfo flash code to use the same delay.  This is
          synchronous, so many bells might inhibit screen updates in other
          windows.
        - text with background==foreground colour gets displayed with default
          bg/fg now when in reverse video, so it can be seen when selecting.
        - allow koi8r* as x11 encoding name for koi8r (Nikita Danilov).
        - removed undocumented inheritPixmapforce option.
        - replaced INSTALL file.