revised patch: tail(1) do not try to reopen stdin

[leo_tck]

Alright, these ones get rid of is_stdin altogether. Isn't it better this
way? 

       --zeurkous.

Index: src/usr.bin/tail/extern.h
===================================================================
RCS file: /cvs/src/usr.bin/tail/extern.h,v
retrieving revision 1.12
diff -u -p -r1.12 extern.h
--- src/usr.bin/tail/extern.h   19 Nov 2015 17:50:04 -0000      1.12
+++ src/usr.bin/tail/extern.h   3 Jan 2019 10:00:59 -0000
@@ -55,4 +55,3 @@ void oerr(void);
 void printfname(const char *);
 
 extern int fflag, rflag, rval;
-extern int is_stdin;

Index: src/usr.bin/tail/forward.c
===================================================================
RCS file: /cvs/src/usr.bin/tail/forward.c,v
retrieving revision 1.31
diff -u -p -r1.31 forward.c
--- src/usr.bin/tail/forward.c  5 Jul 2016 05:06:27 -0000       1.31
+++ src/usr.bin/tail/forward.c  3 Jan 2019 10:00:59 -0000
@@ -335,7 +335,8 @@ tfreopen(struct tailfile *tf) {
        struct tailfile                 **treopen, *ttf;
        int                               i;
 
-       if (tf && ((stat(tf->fname, &sb) != 0) || sb.st_ino != tf->sb.st_ino)) {
+       if (tf && !(tf->fp == stdin) &&
+           ((stat(tf->fname, &sb) != 0) || sb.st_ino != tf->sb.st_ino)) {
                if (afiles < ++nfiles) {
                        afiles += AFILESINCR;
                        treopen = reallocarray(reopen, afiles, sizeof(*reopen));

Index: src/usr.bin/tail/tail.c
===================================================================
RCS file: /cvs/src/usr.bin/tail/tail.c,v
retrieving revision 1.21
diff -u -p -r1.21 tail.c
--- src/usr.bin/tail/tail.c     3 Feb 2016 12:23:57 -0000       1.21
+++ src/usr.bin/tail/tail.c     3 Jan 2019 10:00:59 -0000
@@ -45,7 +45,6 @@
 #include "extern.h"
 
 int fflag, rflag, rval;
-int is_stdin;
 
 static void obsolete(char **);
 static void usage(void);
@@ -173,7 +172,6 @@ main(int argc, char *argv[])
 
                tf[0].fname = "stdin";
                tf[0].fp = stdin;
-               is_stdin = 1;
 
                if (fstat(fileno(stdin), &(tf[0].sb))) {
                        ierr(tf[0].fname);