add UPGRADENEEDED error code

lib/server.js

@@ -1396,7 +1396,7 @@ WalletService.prototype.getPendingTxs = function(opts, cb) {
         return _.startsWith(txp.version, '1.');
       });
 
-      if (!allLegacy) return cb(new Error('Some spend proposals were created using a newer version. Please upgrade your client app.'))
+      if (!allLegacy) return cb(new ClientError('UPGRADENEEDED', 'Some spend proposals were created using a newer version of the client app'));
     }
 
     _.each(txps, function(txp) {

test/integration/server.js

@@ -4309,7 +4309,8 @@ describe('Wallet service', function() {
               server.getPendingTxs({}, function(err, txps) {
                 should.exist(err);
                 should.not.exist(txps);
-                err.toString().should.contain('created by a newer version');
+                err.code.should.equal('UPGRADENEEDED');
+                err.message.should.contain('newer version');
                 done();
               });
             });