test_signal.rb: use SIGINT if needed

* test/ruby/test_signal.rb (test_kill_immediately_before_termination):
  use SIGINT if SIGUSR1 is not available.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41441 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_signal.rb: use standard fds

* test/ruby/test_signal.rb (test_exit_action): use IO.popen and
  standard file descriptors instead of fd 3 and 4, which is not
  available on Windows.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41442 b2dd03c8-39d4-4d8f-98ff-823fe69b080e