Listen for method definition on Kernel and undefine on Namespace

Fixes capture method issues when ActiveSupport Kernel extensions are
loaded after a namespace is defined.

lib/capistrano/configuration/namespaces.rb

@@ -214,3 +214,23 @@ def explicitly_define_clashing_kernel_methods
     end
   end
 end
+
+module Kernel
+  class << self
+    alias_method :method_added_without_capistrano, :method_added
+
+    # Detect method additions to Kernel and remove them in the Namespace class
+    def method_added(name)
+      result = method_added_without_capistrano(name)
+      return result if self != Kernel
+
+      namespace = Capistrano::Configuration::Namespaces::Namespace
+
+      if namespace.method_defined?(name) && namespace.method(name).owner == Kernel
+        namespace.send :undef_method, name
+      end
+
+      result
+    end
+  end
+end

test/configuration/namespace_dsl_test.rb

@@ -322,8 +322,6 @@ def some_weird_method() 'config' end
       def some_weird_method() 'kernel' end
     end
 
-    @config.namespace(:clash2) {}
-    namespace = @config.namespaces[:clash2]
     assert_equal 'config', namespace.some_weird_method
 
     Kernel.send :remove_method, :some_weird_method