Make _.include/_.contains work with strings.

test/collections.js

@@ -164,6 +164,11 @@ $(document).ready(function() {
     ok(!_.include([1,3,9], 2), 'two is not in the array');
     ok(_.contains({moe:1, larry:3, curly:9}, 3) === true, '_.include on objects checks their values');
     ok(_([1,2,3]).include(2), 'OO-style include');
+    ok(_.include('test this out', 'out'), 'include with a string');
+    ok(!_.include('test this out', 'not included'), 'include with a string (false)');
+    ok(_.include('1 2 3 4', 3), 'include with a string and number');
+    ok(_.include(new String('test this'), 'test'), 'works with boxed strings');
+    ok(_('test this out').include('this'), 'OO-style include with a string');
   });
 
   test('collections: invoke', function() {

underscore.js

@@ -198,11 +198,13 @@
   };
 
   // Determine if a given value is included in the array or object using `===`.
-  // Aliased as `contains`.
+  // Aliased as `contains`.  Or if `obj` is a string, test if the string contains the
+  // substring.
   _.include = _.contains = function(obj, target) {
     var found = false;
     if (obj == null) return found;
     if (nativeIndexOf && obj.indexOf === nativeIndexOf) return obj.indexOf(target) != -1;
+    if (_.isString(obj)) return obj.indexOf(target) != -1;
     found = any(obj, function(value) {
       return value === target;
     });
@@ -832,7 +834,7 @@
       return toString.call(obj) == '[object ' + name + ']';
     };
   });
-  
+
   // Define a fallback version of the method in browsers (ahem, IE), where
   // there isn't any inspectable "Arguments" type.
   if (!_.isArguments(arguments)) {