trail rejection fixes


git-svn-id: https://gnunet.org/svn/gnunet@34175 140774ce-b5e7-0310-ab8b-a85725594a96
sensor: test case for proof-of-work + fixes


git-svn-id: https://gnunet.org/svn/gnunet@34176 140774ce-b5e7-0310-ab8b-a85725594a96