(trunk, libT) #4160 'foreign character support' -- merge mike.dld's 4160-03a-file.platch, which introduces tr_sys_file_*() portability wrappers

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14321 f4695dd4-2c0a-0410-b89c-da849a56a58e