bump to 2.81 + first pass at 2.81 NEWS

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14126 f4695dd4-2c0a-0410-b89c-da849a56a58e
tweak NEWS

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14127 f4695dd4-2c0a-0410-b89c-da849a56a58e