* nis/nss: Document SETENT_BATCH_READ.
* nis/libnsl.h: Define NSS_FLAG_SETENT_BATCH_READ.
* nis/nss_nis/nis-service.c (saveit): Don't add NUL byte if the
string is already NUL terminated.
(internal_nis_endservent): No need to return anything. Change callers.
(internal_nis_setservent): One more initialization.
* nis/nss_nis/nis-pwd.c: Support SETENT_BATCH_READ option.
* nis/nss_nis/nis-grp.c: Likewise.
* nis/nss-default.c (init): Rewrite parser to get the variables
