Update GNU tar error code documentation.

Backpatch to 8.2.X.

doc/src/sgml/backup.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.99 2007/07/16 22:20:51 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.100 2007/09/14 04:15:50 momjian Exp $ -->
 
 <chapter id="backup">
  <title>Backup and Restore</title>
@@ -729,16 +729,17 @@ SELECT pg_stop_backup();
    <para>
     Some backup tools that you might wish to use emit warnings or errors
     if the files they are trying to copy change while the copy proceeds.
-    This situation is normal, and not an error, when taking a base backup of
-    an active database; so you need to ensure that you can distinguish
+    This situation is normal, and not an error, when taking a base backup
+    of an active database; so you need to ensure that you can distinguish
     complaints of this sort from real errors.  For example, some versions
-    of <application>rsync</> return a separate exit code for <quote>vanished
-    source files</>, and you can write a driver script to accept this exit
-    code as a non-error case.  Also, some versions of GNU
-    <application>tar</> consider it an error if a file is changed while
-    <application>tar</> is copying it.  Fortunately, GNU
-    <application>tar</> versions 1.16 and later exit with <literal>1</>
-    if files changed during the backup, and <literal>2</> for other errors.
+    of <application>rsync</> return a separate exit code for
+    <quote>vanished source files</>, and you can write a driver script to
+    accept this exit code as a non-error case.  Also, some versions of
+    GNU <application>tar</> consider it an error if a file was truncated
+    while <application>tar</> is copying it.  Fortunately, GNU
+    <application>tar</> versions 1.16 and later exits with <literal>1</>
+    if a file was changed during the backup, and <literal>2</> for other
+    errors.
    </para>
 
    <para>