Fix requirements of silent8.test.

[Ralf Wildenhues]

I'm applying this obvious fix to the jk-silent branch and merging to
master.  (I'll be pushing all of this out later today, I guess.)

Cheers,
Ralf

    Fix requirements of silent8.test.
    
    * tests/silent8.test: Require makeinfo --html, tex, texi2dvi -o,
    dvips.

diff --git a/tests/silent8.test b/tests/silent8.test
index 88f0821..2546775 100755
--- a/tests/silent8.test
+++ b/tests/silent8.test
@@ -16,6 +16,7 @@
 
 # Check texinfo rules in silent-rules mode.
 
+required='makeinfo-html tex texi2dvi-o dvips'
 . ./defs
 
 set -e