evloop could be better at handling fork() in tests

For #28179 (moved) we saw an issue on kqueue() based systems where if tests were run with TT_FORK the event could fail with an invalid FD error message (EBADF).

changed milestone to %Tor: unspecified

added 041-proposed component::core tor/tor milestone::Tor: unspecified priority::medium severity::normal status::new type::enhancement version::tor unspecified labels

The error can be seen here:

https://travis-ci.org/ahf/tor/jobs/471094512

slow/process/callbacks: [forking] [warn] kevent: Bad file descriptor
Dec 21 18:27:55.660 [err] libevent call with kqueue failed: Bad file descriptor [9]
  FAIL src/test/test_process_slow.c:188: assert(ret OP_EQ 0): -1 vs 0
  FAIL src/test/test_process_slow.c:243: assert(smartlist_len(process_data->stdout_data) OP_EQ 12): 0 vs 12
  [callbacks FAILED]
slow/process/callbacks_terminate: [forking] [warn] kevent: Bad file descriptor
Dec 21 18:27:56.036 [err] libevent call with kqueue failed: Bad file descriptor [9]
  FAIL src/test/test_process_slow.c:188: assert(ret OP_EQ 0): -1 vs 0
  FAIL src/test/test_process_slow.c:331: assert(process_data->did_exit)
  [callbacks_terminate FAILED]
2/14 TESTS FAILED. (0 skipped)
FAIL src/test/test-slow (exit status: 1)

Trac:
Sponsor: Sponsor8 to Sponsor19-must

Trac:
Sponsor: Sponsor19-must to N/A

Mark some 0.4.0.x tickets as proposed for 0.4.1.x

Trac:
Keywords: N/A deleted, 041-proposed added
Milestone: Tor: 0.4.0.x-final to Tor: unspecified

Trac:
Parent: #28179 (moved) to N/A

moved to tpo/core/tor#28845 (closed)