Display width 0 wide char with Unicode escape seq.

This change intends to make those characters editable and only
affects the vi editing area; ex messages and vi messages display
them as-is.

Closes-Bug: #10
Fix cleanup multikey mappings (FreeBSD bin/182463)

It's a regression caused by the SLIST migration; the code detects
for multikey (screen-specific) mappings but always delete from
the head of the list.
Remove the stale spell check files.
Transactionally handle the iconv_open failures.

Already opened iconv_t(s) are not affected by failed new encodings.

Closes-Bug: #13
Suppress an uninitialized warning.
Cleanup some whitespace inconsistency.

Also put open curly braces of function body on a new line.
Forgot to touch the year when bumping the version.
Fix a misuse of strncasecmp(3).
Drop UTF-16 write (4334a82 continued).
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
use multibyte.h macros for CHAR_T

this fixes O commands with autoindent and J command at least.