* libmisc/utmp.c: Avoid implicit conversion of pointers / chars to

	* libmisc/utmp.c: Avoid implicit conversion of pointers / chars to
	booleans.
	* libmisc/utmp.c: Add brackets and parenthesis.
	* libmisc/utmp.c: Exit with the EXIT_FAILURE status code in case
	of failure.
	* libmisc/utmp.c: Avoid assignments in comparisons.
	* lib/prototypes.h, libmisc/utmp.c: Change setutmp()'s prototype
	to return an int because pututline() and pututxline() may fail.