- renamed NAT's failure code to status code
- updated status code descriptions
- added NAT library function to convert status codes to strings

git-svn-id: https://gnunet.org/svn/gnunet@33678 140774ce-b5e7-0310-ab8b-a85725594a96
- renamed NAT's failure code to status code across gnunet (not GTK yet)
- added proper error reporting to NAT-test-start/stop
- timed-out nat tests not automatically stop the test itself
- fixed a design flaw in nat-test
- fixed a potential crash in the tests of the nat functionality (NOT NAT_TEST_xy...)

git-svn-id: https://gnunet.org/svn/gnunet@33679 140774ce-b5e7-0310-ab8b-a85725594a96