leakchecker.rb: for older IO.console

* test/lib/leakchecker.rb (check_fd_leak): do not call older
  version IO.console to get rid of ArgumentError, so that older
  versions can run to compare the resuls.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49106 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/lib/leakchecker.rb

@@ -31,8 +31,8 @@ class LeakChecker
   def check_fd_leak(test_name)
     leaked = false
     live1 = @fd_info
-    if IO.respond_to?(:console)
-      IO.console(:close)
+    if IO.respond_to?(:console) and (m = IO.method(:console)).arity.nonzero?
+      m[:close]
     end
     live2 = find_fds
     fd_closed = live1 - live2