epoll_ctl.2, execve.2, recv.2, timer_create.2, wait.2, argz_add.3, basename.3, dlopen...

epoll_ctl.2, execve.2, recv.2, timer_create.2, wait.2, argz_add.3, basename.3, dlopen.3, exec.3, fopencookie.3, fts.3, getaddrinfo.3, getcwd.3, gethostbyname.3, getifaddrs.3, getipnodebyname.3, getlogin.3, getnetent.3, getprotoent.3, getrpcent.3, getservent.3, getusershell.3, glob.3, if_nameindex.3, inet_ntop.3, lio_listio.3, mblen.3, mbrlen.3, mbrtowc.3, mbsinit.3, mbsnrtowcs.3, mbsrtowcs.3, mbstowcs.3, mq_notify.3, ptsname.3, realpath.3, setnetgrent.3, sigvec.3, strsignal.3, strtok.3, wcrtomb.3, wcsnrtombs.3, wcsrtombs.3, wcstombs.3, xdr.3: Global fix of "NULL pointer"

Change "NULL pointer: to "NUL " or null pointer".
POSIX uses the term "null pointer", not "NULL pointer".

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>