Carry ajax error checking from step #13 forward to other ajax steps

The following steps also have an ajax function, but the 'error:' param
is gone after #13:
#14
#17
#19
#20
This may be superfluous, but it helped me find an error with something I
was doing - Namely, in my .json file, I had single line javascript
comments ("//") that I copied from the tutorial. I couldn't find the
issue on later steps, but was able to see my issue when the error
handler complained about an unexpected "/" in my file in step #13.

docs/tutorial.md

@@ -420,6 +420,9 @@ var CommentBox = React.createClass({
       dataType: 'json',
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },
@@ -526,6 +529,9 @@ var CommentBox = React.createClass({
       dataType: 'json',
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },
@@ -593,6 +599,9 @@ var CommentBox = React.createClass({
       dataType: 'json',
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },
@@ -604,6 +613,9 @@ var CommentBox = React.createClass({
       data: comment,
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },
@@ -641,6 +653,9 @@ var CommentBox = React.createClass({
       dataType: 'json',
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },
@@ -655,6 +670,9 @@ var CommentBox = React.createClass({
       data: comment,
       success: function(data) {
         this.setState({data: data});
+      }.bind(this),
+      error: function(xhr, status, err) {
+        console.error(this.props.url, status, err.toString());
       }.bind(this)
     });
   },