Improve listed incremental dumps.

The modified algorithm tries to avoid dumping the same
directory twice and ensures the order of the directories
in the resulting archive is the same, whatever their order
on the command line.  It also fixes the operation of
--listed-incremental -C.

* gnulib.modules: Add canonicalize
* src/common.h (incremental_level): New global.
(check_exclusion_tags): first argument is const.
(get_directory_contents): Add third argument.
(zap_slashes, normalize_filename): New prototypes.
(chdir_count): New prototype.
(WARN_VERBOSE_WARNINGS): New define.
(WARN_ALL): Exclude WARN_VERBOSE_WARNINGS.
* src/compare.c (diff_dumpdir): Update the call to get_directory_contents.
* src/create.c (check_exclusion_tags): First argument is const.
Use ISSLASH and DIRECTORY_SEPARATOR instead of referring to '/'.

* src/incremen.c (struct directory): New member `caname'.
(hash_directory_name): Rename to hash_directory_canonical_name. Operate
on the canonical name.
(compare_directory_names): Rename to compare_directory_canonical_names.
Operate on the canonical name.
(make_directory): Take two arguments.
(free_directory): Free caname.
(attach_directory): Create caname.
(find_directory): Use caname for lookups.
(PD_VERBOSE): Remove.
(PD_FORCE_INIT): New define.
(procdir): First argument is const.
Reinitialize directory if PD_FORCE_INIT bit is set.
Do not use PD_VERBOSE or verbose_option for issuing warnings.
Rely on WARNOPT instead.
Always set *entry.
(scan_directory): Take three arguments. The third one is a boolean
which is true if the directory is explicitly mentioned on the command
line.
(get_directory_contents): Remove.  Use scan_directory instead.
All callers updated.
(read_directory_file): Truncate the file if --level=0 is given.
* src/misc.c: Include canonicalize.h
(zap_slashes, normalize_filename): New functions.
(chdir_count): New function.
* src/names.c (add_hierarchy_to_namelist): Take three arguments, as
get_directory_contents and scan_directory.
(collect_and_sort_names): Allow at most one -C, before file name
arguments.
Read directory file after eventual changing to another directory.
Avoid adding the same directory under different pathnames to
the list.
* src/tar.c: New option --level.

* tests/incr03.at, tests/incr04.at, tests/listed01.at,
tests/listed02.at, tests/rename01.at, tests/rename02.at,
tests/rename03.at: Update for new tar behavior.
* tests/multiv01.at: Do not use --listed-incremental.