patch 8.2.3590: test for v:colornames sometimes fails

Problem:    Test for v:colornames sometimes fails. (Dominique Pellé)
Solution:   Check features.  Clear v:colornames between tests. (Drew Vogel,
            closes #9105, closes #9073)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index d072f34..88b6f0d 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1871,7 +1871,7 @@
 		by setting it in their |.vimrc|.
 
 		It is possible to remove entries from this dictionary but
-		doing so is *NOT* recommended. Doing so is disruptive to
+		doing so is NOT recommended, because it is disruptive to
 		other scripts. It is also unlikely to achieve the desired
 		result because the |:colorscheme| and |:highlight| commands will
 		both automatically load all `colors/lists/default.vim` color