Log Message:
Update mksh to R51. From Changelog:

[tg] OpenBSD sync: handle integer base out of band like ksh93 does
[tg] Protect standard code (predefined aliases, internal code, aliases and \ 
functions in dot.mkshrc) from being overridden by aliases and, in some cases, \ 
shell functions (i.e. permit overriding but ignore it)
[tg] Implement GNU bash's enable for dot.mkshrc using magic aliases to redirect \ 
the builtins to external utilities; this differs from GNU bash in that enable \ 
takes precedence over functions
[tg] Move unaliasing an identifier when defining a POSIX-style function with the \ 
same name into lksh, as compatibility kludge
[tg] Korn shell style functions now have locally scoped shell options
[tg, iSKUNK] Change some ASCII-isms to be EBCDIC-aware or pluggable
[tg, Ypnose] Mention lksh build instructions on manpage and website
[tg] Overhaul signal handling; support new POSIX NSIG_MAX, add sysconf(_SC_NSIG) \ 
as a later TODO item
[tg] Fix signal bounds (1 <= signum < NSIG)
[tg] Improve manual pages, especially wrt. standards compliance
[tg, iSKUNK] Initial EBCDIC work for dot.mkshrc
[tg, iSKUNK] Add list of z/OS signals to Build.sh
[tg] Work around the sh(1) backslash-newline problem by moving the code \ 
triggering it out of *.opt and into the consumers
[colona] Bind another well-known ANSI Del key in the Emacs mode
[tg] Fix ${foo/*/x} pattern checks, spotted by izabera
[carstenh] Fix error output of cd function in dot.mkshrc
[tg] read partial returns in -N and timeout cases
[tg] Fix $LINENO inside PS1; spotted by carstenh
[tg] Ensure correct padding of at least 2 spaces in print_columns
[tg] Note issues with nested complex parameter expansions and follow-up bugfixes \ 
to expect
[OpenBSD] Some language fixes in documentation; comments
[tg] Reimplement multi-line command history (Debian #783978) + fixes
[Martijn Dekker] Fix command -v for "shell reserved words"
[tg] In dot.mkshrc make use of latest feature: local options
[tg] Fix ""$@ to emit a word
[tg] Change cat(1) hack to look first and not ignore builtin
[KO Myung-Hun] Begin porting mksh to OS/2
[komh, tg] Some generic minor bugfixes from OS/2 porting
[tg] Document mknod(8) isn’t normally part of mksh(1)
[tg] Quote arguments to : in build/test scripts as well
[tg] Add cat(1) hack for printf(1)-as-builtin: always prefer external
[tg] Explicitly use binary mode for any and all file I/O in stock mksh
[Ilya Zakharevich] Use termio, not termios(4), on OS/2
[tg] Set edchars to sane BSD defaults if any are NUL
[tg] Implement support for PC scancodes in Vi and Emacs editing mode
[komh] OS/2 uses ; as PATH separator plus support drive letters