Report positional options that were used but had no effect during archive creation

* src/names.c (file_selection_option)
(file_selection_option_name): New functions.
(unconsumed_option_push, unconsumed_option_free)
(unconsumed_option_report): New functions.
(name_list_advance): Maintain a list
of eventually unconsumed options during archive creation.
Report unconsumed options, if any.

* tests/positional01.at: New test case.
* tests/positional02.at: New test case.
* tests/positional03.at: New test case.
* tests/Makefile.am: Add new test cases.
* tests/testsuite.at: Likewise.

* NEWS: Document the changes.
* configure.ac: Version 1.29.90
* doc/tar.texi: Document the changes.

doc/tar.texi

@@ -3879,6 +3879,23 @@ tar -cf a.tar /usr --no-recursion /var/*
 tar -cf a.tar --recursion /usr --no-recursion /var/*
 @end example
 
+During archive creation, @GNUTAR{} keeps track of positional options
+used and arguments affected by them.  If it finds out that any such
+options are used in an obviously erroneous way, the fact is reported
+and exit code is set to 2.  E.g.:
+
+@example
+@group
+$ @kbd{tar -cf a.tar . --exclude '*.o'}
+tar: The following options were used after any non-optional
+arguments in archive create or update mode.  These options are
+positional and affect only arguments that follow them.  Please,
+rearrange them properly.
+tar: --exclude '*.o' has no effect
+tar: Exiting with failure status due to previous errors
+@end group
+@end example
+
 The following table summarizes all position-sensitive options. 
 
 @table @option