* src/vipw.c: Use a bool when possible instead of int integers.

	* src/vipw.c: Use a bool when possible instead of int integers.
	* src/vipw.c: Ignore the return value of umask(), when the mask is
	set again to the old value.
	* src/vipw.c: Avoid implicit conversion of pointers / integers to
	booleans.
	* src/vipw.c: Add brackets and parenthesis.
	* src/vipw.c: Avoid assignments in comparisons.
	* src/vipw.c: Ignore return value of setlocale(),
	bindtextdomain(), and textdomain().
	* src/vipw.c: Add missing termination of the longopts parameter
	for getopt_long().