tar: go back to absolutifying filenames in normalize_filename for now

* src/misc.c (normalize_filename): For now, go back to making
filenames absolute, even though this causes 'tar' to fail when
getcwd fails.  However, do not attempt to resolve ".." as this
does not work with symlinks.  Also, do the right thing with
leading file system prefixes and on hosts where // != /.

src/misc.c

@@ -278,7 +278,32 @@ normalize_filename_x (char *file_name)
 char *
 normalize_filename (const char *name)
 {
-  char *copy = xstrdup (name);
+  char *copy = NULL;
+
+  if (IS_RELATIVE_FILE_NAME (name))
+    {
+      /* Set COPY to the absolute file name if possible.
+
+         FIXME: There should be no need to get the absolute file name.
+         getcwd is slow, it might fail, and it does not necessarily
+         return a canonical name even when it succeeds.  Perhaps we
+         can use dev+ino pairs instead of names?  */
+      copy = xgetcwd ();
+      if (copy)
+        {
+          size_t copylen = strlen (copy);
+          bool need_separator = ! (DOUBLE_SLASH_IS_DISTINCT_ROOT
+                                   && copylen == 2 && ISSLASH (copy[1]));
+          copy = xrealloc (copy, copylen + need_separator + strlen (name) + 1);
+          copy[copylen] = DIRECTORY_SEPARATOR;
+          strcpy (copy + copylen + need_separator, name);
+        }
+      else
+        WARN ((0, errno, _("Cannot get working directory")));
+    }
+
+  if (! copy)
+    copy = xstrdup (name);
   normalize_filename_x (copy);
   return copy;
 }