* include/ruby/win32.h (rb_w32_aspawn_flags): add the declaration of
	  new function.

	* process.c (enum): add EXEC_OPTION_PGROUP and move the position
	  above for the usage in proc_spawn_n().

	* process.c (proc_spawn_n): add an argument to pass new option
	  `new_pgroup`. The option specifies CREATE_NEW_PROCESS_GROUP flag to
	  CreateProcessW(). This flag is necessary for the usage of
	  Process.kill on the subprocess on Windows.

	* process.c (rb_exec_arg_addopt): ditto.

	* process.c (rb_spawn_process): ditto.

	* process.c (documentation for rb_f_spawn): add documentation for new
	  option `new_pgroup` of spawn.

	* test/ruby/test_process.rb (TestProcess#test_execopts_new_pgroup):
	  add tests for option `new_pgroup`.

	* test/ruby/test_thread.rb
	  (TestThreadGroup#test_thread_timer_and_interrupt):
	  add option `new_pgroup: true` to spawn on Windows. It's needed for
	  Process.kill on a subprocess.

	* win32/win32.c (CreateChild): add an argument to pass
	  dwCreationFlags of CreateProcessW().

	* win32/win32.c (rb_w32_spawn): ditto.

	* win32/win32.c (rb_w32_aspawn_flags): add new function to pass
	  dwCreationFlags.

	* win32/win32.c (rb_w32_aspawn): refactor to move the content to
	  rb_w32_aspawn_flags().
	  [ruby-core:43245][Bug #6131]

	* test/ruby/test_thread.rb
	  (TestThreadGroup#test_thread_timer_and_interrupt): skip on Windows.
	  Process.kill cannot kill a subprocess if CREATE_NEW_PROCESS_GROUP
	  flag is not specified in a call to CreateProcessW().

	* win32/win32.c (CreateChild): revert the usage of
	  CREATE_NEW_PROCESS_GROUP flag for compatibility.
	  [ruby-core:43245][Bug #6131]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@35332 b2dd03c8-39d4-4d8f-98ff-823fe69b080e