* src/usermod.c: Split update_files() into update_lastlog() and

	* src/usermod.c: Split update_files() into update_lastlog() and
	update_faillog(). Report errors (but don't fail) if the file
	exist, but open(), lseek(), read(), write(), or close() fails.
	* src/usermod.c: Add brackets and parenthesis.
	* src/usermod.c: Ignore the return value of pam_end() before
	exiting.
	* src/usermod.c: Ignore the return value of strftime(),
	snprintf(), and puts().
	* src/usermod.c: Check the return value of gmtime() and asctime(),
	and output the raw time_t on failures.