Use prepend instead of include for helpers. Fixes #1213 (#1214)

lib/sinatra/base.rb

@@ -1439,7 +1439,7 @@ def unlink(path, opts = {}, &bk)  route 'UNLINK',  path, opts, &bk end
       # in `extensions` available to the handlers and templates
       def helpers(*extensions, &block)
         class_eval(&block)   if block_given?
-        include(*extensions) if extensions.any?
+        prepend(*extensions) if extensions.any?
       end
 
       # Register an extension. Alternatively take a block from which an

sinatra-contrib/lib/sinatra/namespace.rb

@@ -232,7 +232,7 @@ def self.prefixed(*names)
 
       def helpers(*extensions, &block)
         class_eval(&block) if block_given?
-        include(*extensions) if extensions.any?
+        prepend(*extensions) if extensions.any?
       end
 
       def register(*extensions, &block)

test/helpers_test.rb

@@ -1947,5 +1947,27 @@ def foo
       assert ok?
       assert_equal '42 < 43', body
     end
+
+    it 'prepends modules so previously-defined methods can be overridden consistently' do
+      mock_app do
+        helpers do
+          def one; nil end
+          def two; nil end
+        end
+
+        helpers ::HelperOne do
+          def two; '2' end
+        end
+
+        get('/one') { one }
+        get('/two') { two }
+      end
+
+      get '/one'
+      assert_equal '1', body
+
+      get '/two'
+      assert_equal '2', body
+    end
   end
 end