Fix compiler warnings:

* libmisc/audit_help.c: Include prototypes.h to get the prototype
	of audit_help_open.
	* libmisc/salt.c: Use booleans instead of negating integers.
	* src/passwd.c: Declare the check_selinux_access prototype and
	avoid name clashes (change_user -> changed_user; change_uid ->
	changed_uid; access -> requested_access)

libmisc/audit_help.c

@@ -44,6 +44,7 @@
 #include <libaudit.h>
 #include <errno.h>
 #include <stdio.h>
+#include "prototypes.h"
 int audit_fd;
 
 void audit_help_open (void)