Make IDs *always* 16 characters

lib/util.js

@@ -22,7 +22,7 @@ var util = {
     return dest;
   },
   randomId: function () {
-    return Math.random().toString(36).substr(2);
+    return (Math.random().toString(36) + '0000000000000000000').substr(2, 16);
   },
   prettyError: function (msg) {
     if (util.debug) {

test/server.js

@@ -206,7 +206,7 @@ describe('PeerServer', function() {
     });
 
     it('should generate a 16-character ID', function() {
-      expect(p._generateClientId('anykey').length).to.be.within(15, 16);
+      expect(p._generateClientId('anykey').length).to.be(16);
     });
   });
 });