replace missing and unsupported flags with output.valid, similar to each loops below

lib/server.js

@@ -836,19 +836,25 @@ WalletService.prototype.createTx = function(opts, cb) {
   if (opts.type == Model.TxProposal.Types.MULTIPLEOUTPUTS) {
     if (!Utils.checkRequired(opts, ['outputs']))
       return cb(new ClientError('Required argument missing'));
-    var missing = false, unsupported = false;
     _.each(opts.outputs, function(o) {
-      if (!Utils.checkRequired(o, ['toAddress', 'amount']))
-        missing = true;
+      o.valid = true;
+      if (!Utils.checkRequired(o, ['toAddress', 'amount'])) {
+        o.valid = false;
+        cb(new ClientError('Required outputs argument missing'));
+        return false;
+      }
       _.each(_.keys(o), function(key) {
-        if (!_.contains(['toAddress', 'amount', 'message'], key))
-          unsupported = true;
+        if (!_.contains(['toAddress', 'amount', 'message', 'valid'], key)) {
+          o.valid = false;
+          cb(new ClientError('Invalid outputs argument found'));
+          return false;
+        }
       });
+      if (!o.valid) return false;
     });
-    if (missing)
-      return cb(new ClientError('Required outputs argument missing'));
-    if (unsupported)
-      return cb(new ClientError('Invalid outputs argument found'));
+    if (_.any(opts.outputs, 'valid', false)) return;
+    _.each(opts.outputs, function(o) { delete o.valid; });
+
   } else {
     if (!Utils.checkRequired(opts, ['toAddress', 'amount']))
       return cb(new ClientError('Required argument missing'));