Add conf_enable_app to add items to $enabled_apps, used from conf_enable_xxx functions so one doesn't need to both add stuff to $eanbled_apps and then call conf_enable_xxx, and to avoid enabling the same app twice.

New conf_enable_wiki function to follow the interface of other apps.

bin/wercconf.rc

@@ -10,3 +10,10 @@ fn conf_hide_paths {
     for(i in $*)
        dirfilter=$dirfilter^'/'^`{echo $i|sed 's!/!\\/!g'}^'/d; '
 }
+
+# Usually will be called from within conf_enable_foo 
+fn conf_enable_app {
+    # Note: maybe we should add test -d apps/$1/?
+    if(! ~ $1 $enabled_apps)
+	enabled_apps=( $enabled_apps $1 )
+}