Work around inability to set highlighting right for urxvt

Vim under urxvt does not seem to react to highlight settings, keeping
defaults that under my favorite scheme make Search unreadable and
MatchParen confusing.

The dirty hack is to re-set the colors it happens to use: Yellow and
Cyan.  Ugly, bad, but will work for now.

dotfiles.config/Xlib/colorscheme/zenburn.Xdefaults

 URxvt.color3:           #dfaf8f
 URxvt.color4:           #506070
 URxvt.color5:           #dc8cc3
-URxvt.color6:           #8cd0d3
+URxvt.color6:           #467071
 URxvt.color7:           #DCDCCC
 URxvt.color8:           #808080
 URxvt.color9:           #cc9393
 URxvt.color10:          #7f9f7f
-URxvt.color11:          #f0dfaf
+URxvt.color11:          #906959
 URxvt.color12:          #94bff3
 URxvt.color13:          #ec93d3
 URxvt.color14:          #93e0e3