Add local copies of the validator buttons

buttons/Makefile

@@ -1,5 +1,5 @@
 FILES = about.png events.png gitweb.png gopher.png home.png library.png \
 	mailman.png media.png office.png services.png stats.png webmail.png \
-	wiki.png valid-atom.png
+	wiki.png valid-atom.png valid-css.png valid-xhtml11.png
 RELDIR = buttons/
 include ../common.mk

xsl/common.xsl

@@ -102,12 +102,12 @@
     </div>
     <p>
       <a href="http://validator.w3.org/check?uri=referer">
-      <img src="http://www.w3.org/Icons/valid-xhtml11"
+      <img src="{$g_pre}buttons/valid-xhtml11.png"
           alt="Valid XHTML 1.1" height="31" width="88" />
       </a>
       <a href="http://jigsaw.w3.org/css-validator/check/referer">
       <img style="border:0;width:88px;height:31px"
-          src="http://jigsaw.w3.org/css-validator/images/vcss"
+          src="{$g_pre}buttons/valid-css.png"
           alt="Valid CSS!" />
       </a>
       <a href="http://validator.w3.org/feed/check.cgi?url=http%3A//csclub.uwaterloo.ca/events.atom">