Licensing changes:

1. add the option the code to be used under GPLv2 or GPLv3; previously only GPLv2 was allowed

2. add the "proxy option" as described in GPLv3 so we can add future licenses without having to bulk-edit everything again :)

3. remove the awkward "exception for MIT code in Mac client" clause; it was unnecessary and confusing.



git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14225 f4695dd4-2c0a-0410-b89c-da849a56a58e