Fix some compilation warnings:

* src/login.c: "dereferencing type-punned pointer will break
   strict-aliasing rules", add a variable indirection: ptr_pam_user.
 * lib/commonio.c: do not initialize the sb stat structure.
 * lib/pwio.c, lib/shadowio.c, lib/sgroupio.c, lib/groupio.c:
   initialize the security context if WITH_SELINUX.
 * lib/nscd.c: The service argument is not const (used in the exec*
   parameters). This matches with the prototype definition.
 * src/groupmems.c: Avoid ++i when i is also used in the same line.
 * src/newusers.c: i is positive every time it is compared. Add
   cast to unsigned int.
 * src/nologin.c: Use a main() prototype with no arguments.
 * libmisc/getdate.y: Initialize the type and value fields of the
   terminating entry for each TABLE.
 * libmisc/tz.c: Use "TZ=CST6CDT" as the default timezone.

libmisc/tz.c

@@ -45,7 +45,7 @@ char *tz (const char *fname)
 {
 	FILE *fp = 0;
 	static char tzbuf[BUFSIZ];
-	const char *def_tz;
+	const char *def_tz = "TZ=CST6CDT";
 
 	if ((fp = fopen (fname, "r")) == NULL ||
 	    fgets (tzbuf, sizeof (tzbuf), fp) == NULL) {