* include/am_defs.h: define extern for sleep(3) if needed.

* include/am_defs.h: define extern for sleep(3) if needed.

* m4/macros/header_templates.m4: template for sleep(3) extern.

* configure.in: check for extern for sleep(3), which is missing
from some old (and buggy) versions of gcc's fixinc'ed headers.

* conf/nfs_prot/nfs_prot_aix4_3.h: update definition of struct
nfs_args from actual system headers.

* conf/mount/mount_aix.c (mount_aix3): fix name of aix4 "bis"
structure.