Filter out previous definition warnings

Author: petergoldstein

example_app_generator/spec/verify_mailer_preview_path_spec.rb

@@ -23,6 +23,7 @@ def capture_exec(*ops)
               .reject { |line| line =~ /warning: circular argument reference/ }
               .reject { |line| line =~ /Gem::Specification#rubyforge_project=/ }
               .reject { |line| line =~ /DEPRECATION WARNING/ }
+              .reject { |line| line =~ /warning: previous/ }
               .join
               .chomp
     CaptureExec.new(out, $?.exitstatus)