Pull up the following revisions(s) (requested by martin in ticket #1023):
	lib/libc/gen/posix_spawn.3:			revision 1.5
	lib/libc/gen/posix_spawn_file_actions_addopen.3:	revision 1.4
	lib/libc/gen/posix_spawn_file_actions_init.3:	revision 1.4
	lib/libc/gen/posix_spawn_fileactions.c:		revision 1.3
	sys/compat/netbsd32/netbsd32_execve.c:		revision 1.38
	sys/kern/kern_exec.c:				revision 1.373

Limit the amount of kernel memory a posix_spawn syscall can use (for
handling the file action list) by limiting the maximum number of file
actions to twice the current file descriptor limit. Fix a few bugs in
the support functions and document the new limit. From Maxime Villard.
Ticket #1023