tar: don't crash if getcwd fails

* src/extract.c: Don't include xgetcwd.h.
(extract_dir): stat "." rather than statting getcwd's output.
* src/misc.c (normalize_filename_x): Rewrite so as not to resolve
/../, which can't be done reliably in the presence of symlinks.
Don't reject valid names such as ".".
(normalize_filename): Don't make it absolute; that way, we don't
have to invoke xgetcwd which might fail.  Don't bother to realloc
at the end, since that uses time and now saves little space.
(chdir_do): Don't crash if xgetcwd fails.
* tests/Makefile.am (TESTSUITE_AT): Add listed03.at.
* tests/listed03.at: New file.
* tests/testsuite.at: Include listed03.at.

src/extract.c

@@ -23,7 +23,6 @@
 #include <quotearg.h>
 #include <utimens.h>
 #include <errno.h>
-#include <xgetcwd.h>
 #include <priv-set.h>
 
 #include "common.h"
@@ -648,13 +647,11 @@ extract_dir (char *file_name, int typeflag)
   if (one_file_system_option && root_device == 0)
     {
       struct stat st;
-      char *dir = xgetcwd ();
 
-      if (deref_stat (true, dir, &st))
-	stat_diag (dir);
+      if (stat (".", &st) != 0)
+	stat_diag (".");
       else
 	root_device = st.st_dev;
-      free (dir);
     }
 
   if (incremental_option)