Introducing Message4. The changes to the related sources are ifdefed with USING_MESSAGE4 which is defined in Message4.h. To use Message4 the Message4.cpp, Message4.h, MessageUtils4.cpp, MessageUtils4.h and MessagePrivate4.h have to be linked to their counterparts without 4 suffix. Then MessageBody.cpp and MessageField.cpp have to be commented out in the app kit Jamfile and r5_message.cpp has to be added. There remain some bugs to be found. Feel free to change that.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@14882 a95241bf-73f2-0310-859d-f6bbb57e9c96
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