bump version to 2.81+

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14129 f4695dd4-2c0a-0410-b89c-da849a56a58e
add tr_sessionGetTorrents(), a private utility to avoid code duplication in libtransmission

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14130 f4695dd4-2c0a-0410-b89c-da849a56a58e