Add another file check to check_for_macgpg2

Library/Homebrew/brew_doctor.rb

@@ -31,7 +31,8 @@ end
 # Installing MacGPG2 interferes with Homebrew in a big way
 # http://sourceforge.net/projects/macgpg2/files/
 def check_for_macgpg2
-  if File.exist? "/Applications/start-gpg-agent.app"
+  if File.exist? "/Applications/start-gpg-agent.app" or
+     File.exist? "/Library/Receipts/libiconv1.pkg"
     puts <<-EOS.undent
       If you have installed MacGPG2 via the package installer, several other
       checks in this script will turn up problems, such as stray .dylibs in