Don't treat run() as a parallel task

Fixes a regression from #457

lib/capistrano/configuration/actions/invocation.rb

@@ -320,7 +320,7 @@ module Capistrano
               branches += server_branches
             end
             branches
-          end
+          end.compact.uniq
         end
 
       end

test/configuration/actions/invocation_test.rb

@@ -243,6 +243,12 @@ class ConfigurationActionsInvocationTest < Test::Unit::TestCase
 
   def test_parallel_command_execution_with_matching_servers
     @config.expects(:execute_on_servers)
+
+    logger = mock('logger')
+    logger.stubs(:debug).with("executing multiple commands in parallel").once
+    logger.stubs(:trace).twice
+    @config.stubs(:logger).returns(logger)
+
     assert_block("should not raise Argument error") do
       begin
         @config.servers = [:app, :db]
@@ -258,6 +264,18 @@ class ConfigurationActionsInvocationTest < Test::Unit::TestCase
     end
   end
 
+  def test_run_only_logs_once
+    @config.servers = [:app, :db]
+
+    logger = mock('logger')
+    logger.stubs(:debug).with("executing \"ls\"")
+    @config.stubs(:logger).returns(logger)
+
+    @config.expects(:execute_on_servers)
+
+    @config.run("ls")
+  end
+
   private
 
     def make_config