Use EINVAL instead of EDOOFUS. Add a missing synopsis for
pidfile_fileno() in the man page. Move the definition of struct pidfh
from libutil.h into pidfile.c following upstream change.
Taken from FreeBSD.
Remove MAXPATHLEN from ‘struct pidfh’ and allocate pf_path dynamically,
as some systems do not have such limits. Use dev_t instead of __dev_t.
Replace EDOOFUS with EINVAL.