Constant nc::FD_SETSIZE

pub const FD_SETSIZE: usize

This allows for 1024 file descriptors: if NR_OPEN is ever grown beyond that you'll have to change this too. But 1024 fd's seem to be enough even for such "real" unices like OSF/1, so hopefully this is one limit that doesn't have to be changed [again].

Note that POSIX wants the FD_CLEAR(fd,fdsetp) defines to be in <sys/time.h> (and thus <linux/time.h>) - but this is a more logical place for them. Solved by having dummy defines in <sys/time.h>. This macro may have been defined in <gnu/types.h>. But we always use the one here.