doc: mention the texinfo documentation in --help

doc: mention the texinfo documentation in --help

* src/system.h: Rename emit_bug_reporting_address() to
emit_ancillary_info() and update it to not print the translation
project address in en_* locales, and _do_ print it in the 'C'
(and other) locales so that it's included in the default man page.
Also mention how to invoke the texinfo documentation for each command.
Also move the "hard-locale.h" include to the 8 files that now use it.
* man/help2man: Strip the newly added texinfo reference from the
--help output as a more verbose version is already added by help2man.
Suggestion from C de-Avillez