[Groff] can't use cp866 encoding in groff-1.18

[onk]

HI
We require operation with documents in the encoding cp866/cp1125
(cyrillic chars 0x80..0xAF,0xE0..0xF9).
We have created the tmac.cp866 file with line like
.hcode A A a a
but groff remove chars 0x80..0x9F.

In the invalid.cc file I have found ' invalid _ char _ table [256] ',
where characters 0x80..0x9F marked as invalid.
I have corrected this table, but characters 0x80..0x82, 0x84..0x88
are removed in formatted document.

In version 1.15 this correction works.