maint: update help2man to 1.43.3

maint: update help2man to 1.43.3

Instead of diverging further from the upstream GNU help2man project
(http://www.gnu.org/software/help2man/), hold a copy of the original
script and keep track of our changes in a separate patch file.

The man pages created with the new version show the following,
non-invasive differences:
a) command options in the EXAMPLE sections are no longer in bold format,
b) file names are underlined now consistently.

* man/help2man: Rename to ...
* man/help2man.in: ... this file, and update content from the
upstream GNU help2man project.
* man/help2man.diff: Add patch file for help2man to remove the
sentence "For complete documentation ..." (see commit 5d4f09d8),
and to emit "info coreutils 'PROG invocation'" into the man
pages (77abf69a).
* man/local.mk (mandeps): Add help2man to the dependencies of
the man pages.
(man/help2man): Add rule to generate this script from the upstream
help2man.in file and the help2man.diff patch.
* .gitignore: Add man/help2man as it is no longer version controlled.
* cfg.mk (sc_long_lines): Exempt help2man.in from this check.
(sc_po_check): Likewise.
(sc_space_tab): Likewise.
(sc_trailing_blank): Exempt man/help2man.diff from this check.
(sc_prohibit_tab_based_indentation): Instead of help2man, now exempt
both help2man.in and help2man.diff from this test.
* .x-update-copyright: Add new file and add the above new help2man
files as well as the COPYING file.