I18N bug 1112: Use strange_chars[] for UTF-8 output too

I18N bug 1112: Use strange_chars[] for UTF-8 output too

Make u2cp_() map code points U+0080 to U+009F via strange_chars[] even
if the target codepage is UTF-8.  This helps with buggy web pages that
use ’ when they mean ’.  This change does not affect how
ELinks decodes raw bytes 0x80 to 0x9F in HTML.

u2cp_() is used only via the u2cp and u2cp_no_nbsp macros.
Possible side effects of this change at each use of these macros:

* get_translation_table(): Not affected because it does not call u2cp
  if the target codepage is UTF-8.
* get_entity_string(): Numeric character references are affected, as intended.
  Character entity references are not affected because entities[]
  does not define any entities in the U+0080...U+009F range.
* kbd_field(), term_send_ucs(), field_op(): Affected.  It is no longer
  possible to enter code points U+0080...U+009F from the terminal.
  This should not be a problem in practice because those would be
  control characters anyway and should therefore be filtered by the
  slave process (which doesn't yet recognize them; bug 777).