-m hooked up. test included

Added a test for -m in task.rb. Hooked it up.
Concised code in application.rb
Added documentation for -j

doc/command_line_usage.rdoc

@@ -42,14 +42,15 @@ Options are:
     value is equal to the number of CPUs.
 
     Sample values:
-     default: unlimited concurrent tasks (standard rake behavior)
-     1: one task at a time
+     no -j   : unlimited concurrent tasks (standard rake behavior)
+     only -j : 2 concurrent tasks
+     -j 16   : 16 concurrent tasks
 
 [<tt>--libdir</tt> _directory_  (-I)]
     Add _directory_ to the list of directories searched for require.
 
 [<tt>--multitask</tt> (-m)]
-    Treat all tasks as multitasks. ('make' semantics)
+    Treat all tasks as multitasks. ('make/drake' semantics)
 
 [<tt>--nosearch</tt>  (-N)]
     Do not search for a Rakefile in parent directories.

lib/rake/application.rb

@@ -327,9 +327,7 @@ def standard_rake_options
         ],
         ['--jobs',  '-j [NUMBER]',
           "Specifies the maximum number of tasks to execute in parallel. (default:2)",
-          lambda { |value|
-            options.thread_pool_size = [(value || 2).to_i,2].max
-          }
+          lambda { |value| options.thread_pool_size = [(value || 2).to_i,2].max }
         ],
         ['--libdir', '-I LIBDIR', "Include LIBDIR in the search path for required modules.",
           lambda { |value| $:.push(value) }

lib/rake/task.rb

@@ -172,10 +172,14 @@ def add_chain_to(exception, new_chain)
 
     # Invoke all the prerequisites of a task.
     def invoke_prerequisites(task_args, invocation_chain) # :nodoc:
-      prerequisite_tasks.each { |prereq|
-        prereq_args = task_args.new_scope(prereq.arg_names)
-        prereq.invoke_with_call_chain(prereq_args, invocation_chain)
-      }
+      if application.options.always_multitask
+        invoke_prerequisites_concurrently(task_args, invocation_chain)
+      else
+        prerequisite_tasks.each { |prereq|
+          prereq_args = task_args.new_scope(prereq.arg_names)
+          prereq.invoke_with_call_chain(prereq_args, invocation_chain)
+        }
+      end
     end
 
     def invoke_prerequisites_concurrently(args, invocation_chain)

test/test_rake_task.rb

@@ -223,6 +223,25 @@ def c.timestamp() Time.now + 5 end
     assert_in_delta now + 10, a.timestamp, 0.1, 'computer too slow?'
   end
 
+  def test_all_multitask
+    mx = Mutex.new
+    result = ""
+    root = task :root
+    ('aa'..'zz').each do |c|
+      task(c.to_sym) { mx.synchronize{ result << c } }
+      task(:root => c.to_sym)
+    end
+    root.invoke
+
+    root.prerequisite_tasks.each { |p| p.reenable };
+    root.reenable
+    task_result = result.dup; result.clear
+
+    Rake.application.options.always_multitask = true
+    root.invoke
+    refute_equal task_result, result
+  end
+
   def test_investigation_output
     t1 = task(:t1 => [:t2, :t3]) { |t| runlist << t.name; 3321 }
     task(:t2)