tests: silence test_detect_failed_configure

The standard `nostdout` method doesn't work here because Formula#system
does some redirection of its own; both stdout and stderr have to be of
the same type, so just do it manually here.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/test/test_formula_install.rb

@@ -23,12 +23,22 @@ end
 
 class ConfigureTests < Test::Unit::TestCase
   def test_detect_failed_configure
+    tmperr = $stderr
+    tmpout = $stdout
+    require 'stringio'
+    $stderr = StringIO.new
+    $stdout = StringIO.new
+
     f = ConfigureFails.new
+
     begin
       f.brew { f.install }
     rescue BuildError => e
       assert e.was_running_configure?
     end
+
+    $stderr = tmperr
+    $stdout = tmpout
   end
 end