Problem: Unicode->UJIS followed incorrect conversion
rules for U+00A5 YEN SIGN and U+203E OVERLINE,
so these characters were converted to ujis 0x8E5C
and 0x8E7E accordingly.

This behaviour would be correct for a JIS-X-0201 based character set,
but this is wrong for UJIS, which is documented as x-eucjp-unicode-0.9,
and which is based on ASCII for the range U+0000..U+007F.

Fix:
removing JIS-X-0201 conversion rules, making UJIS ASCII compatible.
YEN SIGN and OVERLINE do not have corresponding UJIS characters anymore
and converted to 0x3F QUESTION MARK, throwing a warning in appropriative cases.

This patch also includes a test covering full UJIS->Unicode->UJIS mapping.