Don't publish mbox_sha1sum in FOAF by default.

We say the email is private data, so reasonably we shouldn't reveal it
indirectly through a hash sum: http://xmlns.com/foaf/spec/#term_mbox_sha1sum

actions/foaf.php

@@ -90,7 +90,7 @@ class FoafAction extends ManagedAction
 
         // Would be nice to tell if they were a Person or not (e.g. a #person usertag?)
         $this->elementStart('Agent', array('rdf:about' => $this->user->getUri()));
-        if ($this->user->email) {
+        if (common_config('foaf', 'mbox_sha1sum') && $this->user->email) {
             $this->element('mbox_sha1sum', null, sha1('mailto:' . $this->user->email));
         }
         if ($this->profile->fullname) {

lib/default.php

@@ -142,6 +142,10 @@ $default =
               'path' => $_path . '/avatar/',
               'ssl' => null,
               'maxsize' => 300),
+        'foaf' =>
+        array(
+              'mbox_sha1sum' => false,
+            ),
         'public' =>
         array('localonly' => false,
               'blacklist' => array(),