Add a large warning for people still using deploy:symlink.

lib/capistrano/configuration/callbacks.rb

@@ -112,6 +112,9 @@ def on(event, *args, &block)
           callbacks[event] << ProcCallback.new(block, options)
         else
           args.each do |name|
+            if name =~ /^(?:deploy\:symlink|symlink)$/
+              Kernel.warn("[API Change] deploy:symlink no longer exists, please use deploy:create_symlink")
+            end
             callbacks[event] << TaskCallback.new(self, name, options)
           end
         end
@@ -145,4 +148,4 @@ def find_hook(task, hook)
 
     end
   end
-end
+end

test/configuration/callbacks_test.rb

@@ -111,6 +111,18 @@ def test_on_with_both_tasks_and_block_should_raise_error
     assert_raises(ArgumentError) { @config.on(:before, :first) { blah } }
   end
 
+  def test_calling_on_before_symlink_should_raise_a_warning
+    Kernel.expects(:warn).with("[API Change] deploy:symlink no longer exists, please use deploy:create_symlink").once
+    task = stub(:fully_qualified_name => "any:old:thing")
+    @config.on(:before, 'deploy:symlink', 'anything')
+  end
+
+  def test_calling_on_after_symlink_should_raise_a_warning
+    Kernel.expects(:warn).with("[API Change] deploy:symlink no longer exists, please use deploy:create_symlink").once
+    task = stub(:fully_qualified_name => "any:old:thing")
+    @config.on(:after, 'deploy:symlink', 'anything')
+  end
+
   def test_trigger_without_constraints_should_invoke_all_callbacks
     task = stub(:fully_qualified_name => "any:old:thing")
     @config.on(:before, :first, "second:third")