(gtk) silence a couple of potential GFileInfo console warnings

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@13811 f4695dd4-2c0a-0410-b89c-da849a56a58e
(trunk) move sandboxed session creation/teardown into libtransmission-test.[ch] so that it can be reused as a fixture by future tests

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@13812 f4695dd4-2c0a-0410-b89c-da849a56a58e