limit the number of FDs in a process for stress test

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52222 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -1135,6 +1135,8 @@ class TestIO < Test::Unit::TestCase
 
   def test_dup_many
     ruby('-e', <<-'End') {|f|
+      lim = Process.getrlimit(Process::RLIMIT_NOFILE)[0]
+      Process.setrlimit(Process::RLIMIT_NOFILE, [lim, 1024].min)
       ok = 0
       a = []
       begin