ATF functions such as ATF_REQUIRE do not work correctly in child processes.
Use plain C functions to report errors instead.
In the parent, check for the untimely demise of children. Without this,
the test hung until the framework's timeout.
Raise the resource limit on the number of open files. If this was too low,
the test hit the two problems above.
Restore the kern.maxfiles sysctl OID in the cleanup function.
The body prematurely removed the symlink in which the old value was saved.
Clean up a temporary file created by the test ("afile").