Fix an incorrect wide buffer length.

The meaning of buffer length was changed from characters count to
bytes count.  This is the only place I found so far which wildly
compares the text length to buffer length.

Closes-Issue: #8
Fill in unsubstituted copyright information.
Fix switching under leftright (FreeBSD bin/12801)
Do not break multibyte chars in ex_prchars.

But vi message output may still break them, especially UTF-8.
Bump version to 2.1.2 in README.
Sync with the OpenBSD manpage, which uses mdoc(7).
port "expandtab" option from NetBSD

http://mail-index.netbsd.org/source-changes/2008/12/12/msg213984.html
http://mail-index.netbsd.org/source-changes/2009/08/07/msg223768.html