New test_select_fd uses a lot of open files

[fliiiix]

I stumbled over this new test from here: 3d1b888

test_inotify_c.py::test_select_fd

   > =========================== short test summary info ============================
   > FAILED tests/test_inotify_c.py::test_select_fd - OSError: [Errno 24] Too many open files: '/build/pytest-of-nixbld/pytest-0/test_select_fd0/new_file'
   > =========== 1 failed, 162 passed, 3 skipped, 3 deselected in 54.20s ============

Which will fails if the ulimit is too low. I naively doubled them from the default 1024 to the 2048 which is still to low for this test.
It would be kinda cool if this test could either fail with a more descriptive error message if the ulimit prevents this test from running successful but ideally i guess it would be even better if that could be tested without exhausting this many open files.