Goal: Provide more info when chown_tty() phase of login fails (see #332198).

Related: #332198 (helps to debug)

Status wrt upstream: Not forwarded (dunno if there's any point in this).

This patch increases verbosity of is_my_tty() routine which is called
from chown_tty() which in turn is part of login sequence. Submitter of
the bug #332198 sometimes gets telnet session refused, but message in
syslog is not at all helpful:
> ... login[453]: unable to determine TTY name, got /dev/pts/1
and in fact it's misleading, because tty name is detected OK, it's
is_my_tty() which is failing for a reason yet unknown (I suspect
corruption of utmp file).

Index: shadow-4.1.0/libmisc/chowntty.c
===================================================================
--- shadow-4.1.0.orig/libmisc/chowntty.c
+++ shadow-4.1.0/libmisc/chowntty.c
@@ -40,6 +40,7 @@
 #include "defines.h"
 #include <pwd.h>
 #include "getdef.h"
+#include <sys/sysmacros.h>
 /*
  * is_my_tty -- determine if "tty" is the same as TTY stdin is using
  */
@@ -47,12 +48,31 @@
 {
 	struct stat by_name, by_fd;
 
-	if (stat (tty, &by_name) || fstat (0, &by_fd))
+	if (stat (tty, &by_name)) {
+		/* Can use neither strerror() nor "%m" sequence -- first
+		 * is locale-dependent (while SYSLOG isn't) and for second
+		 * the SYSLOG macro isn't errno-transparent.  --xrgtn */
+		int e = errno;
+		SYSLOG ((LOG_WARN, "can't stat(`%s'): errno %i\n", tty, e));
 		return 0;
+	}
 
-	if (by_name.st_rdev != by_fd.st_rdev)
+	if (fstat (0, &by_fd)) {
+		int e = errno;
+		SYSLOG ((LOG_WARN, "can't fstat(stdin): errno %i\n", e));
 		return 0;
-	else
+	}
+
+	if (by_name.st_rdev != by_fd.st_rdev) {
+		SYSLOG ((LOG_WARN,
+			 "`%s'.st_rdev(%u,%u) != stdin.st_rdev(%u,%u)\n",
+			 tty,
+			 /* XXX: dev_t is 64bit, gnu_dev_mXXor are used
+			  * which are GNU extn */
+			 major(by_name.st_rdev), minor(by_name.st_rdev),
+			 major(by_fd.st_rdev), minor(by_fd.st_rdev)));
+		return 0;
+	} else
 		return 1;
 }