Make "column"-property of Errors enumerable

Fixes #1284

Appearently, there is a use-case of stringifying the error in order to
evaluated its properties on another system. There was a regression
from 4.0.5  to 4.0.6 that the column-property of compilation errors
was not  enumerable anymore in 4.0.6 (due to  commit 20c965c) and
thus was not included in the output of "JSON.stringify".

lib/handlebars/exception.js

@@ -31,7 +31,10 @@ function Exception(message, node) {
       // Work around issue under safari where we can't directly set the column value
       /* istanbul ignore next */
       if (Object.defineProperty) {
-        Object.defineProperty(this, 'column', {value: column});
+        Object.defineProperty(this, 'column', {
+          value: column,
+          enumerable: true
+        });
       } else {
         this.column = column;
       }

spec/compiler.js

@@ -54,6 +54,15 @@ describe('compiler', function() {
       }
     });
 
+    it('should include the location as enumerable property', function() {
+      try {
+        Handlebars.compile(' \n  {{#if}}\n{{/def}}')();
+        equal(true, false, 'Statement must throw exception. This line should not be executed.');
+      } catch (err) {
+        equal(err.propertyIsEnumerable('column'), true, 'Checking error column');
+      }
+    });
+
     it('can utilize AST instance', function() {
       equal(Handlebars.compile({
         type: 'Program',