Add libintl
test_string: make sure openpty succeeded when running screen-width
dependant tests.
CLD, POLL, PWR are sometimes not available either.
Use standard includes only.
Guard and conditionally include alternative headers.
On kFreeBSD at least, one can set SIGKILL to default handle.
Introduce compat config-freebsd.h header
Remove NIH_C_THREAD from configure.ac
Optionally link inotify library
Disable some PTRACE tests
Disable test_io SCM_CREDENTIALS test
Disable more tests