improve error message when creating/joining over existing wallet file

lib/clilib.js

@@ -78,7 +78,7 @@ CliLib.prototype.createWallet = function(walletName, copayerName, m, n, network,
   var self = this;
 
   var data = this._load();
-  if (data) return cb('Only one wallet is supported in this version');
+  if (data) return cb('File ' + this.filename + ' already contains a wallet');
 
   // Generate wallet key pair to verify copayers
   var privKey = new Bitcore.PrivateKey();
@@ -172,7 +172,7 @@ CliLib.prototype.joinWallet = function(secret, copayerName, cb) {
   var self = this;
 
   var data = this._load();
-  if (data) return cb('Only one wallet is supported in this version');
+  if (data) return cb('File ' + this.filename + ' already contains a wallet');
 
   data = {
     xPrivKey: _createXPrivKey(),