* libmisc/root_flag.c, src/gpasswd.c, src/chsh.c: Add splint

	* libmisc/root_flag.c, src/gpasswd.c, src/chsh.c: Add splint
	annotations.
	* src/pwconv.c, src/pwunconv.c, src/grpconv.c, src/grpunconv.c:
	Ignore return value of spw_rewind, pw_rewind, sgr_rewind, and
	gr_rewind.
	* lib/commonio.h: Both head and tail cannot be owned. Set tail as
	dependent.
	* src/expiry.c: Ignore return value of expire ().
	* src/expiry.c: The catch_signals function does not use its sig
	parameter.
	* src/userdel.c: Last audit_logger parameter is a
	shadow_audit_result, use SHADOW_AUDIT_FAILURE instead of 0.