Upgrade to mksh R56b.

Upgrade to mksh R56b.

R56b is a bugfix-only release everyone should upgrade to:

[tg] Reference the FAQ webpage
[panpo, Riviera] Fix documentation bug wrt. Esc+Ctrl-L
[tg, Larry Hynes] Fix “0” movement in vi mode
[tg] Replace broken libcs’ offsetof macro with MirBSD’s

R56 is a bugfix release with some experimental fixes:

[tg, Seb] Do not apply alias name restrictions to hash/tilde tracking
[tg] Restore ‘.’, ‘:’ and ‘[’ in alias names (“[[” is still forbidden)
[tg] Fix accidentally defanged $PATHSEP test
[tg] On ^C (INTR and QUIT edchars), shove edit line into history
[iSKUNK, tg] Begin porting to z/OS using EBCDIC encoding, incomplete
[tg] Redo fast character classes code, adding POSIX and other helpers
[tg] bind parses backslash-escaped ‘^’ (and ‘\’) as escaped
[tg] Building with -DMKSH_ASSUME_UTF8=0 no longer causes a known failure in the testsuite
[tg] New test.sh option -U to pass a UTF-8 locale to use in the tests
[tg] re_format(7) BSD: [[ $x = *[[:\<:]]foo[[:\>:]]* ]]
[tg, iSKUNK] Use Config in check.pl only if it exists
[tg] New matching code for bracket expressions, full POSIX (8bit)
[komh] Exclude FAT/HPFS/NTFS-unsafe tests on OS/2 (and Cygwin/MSYS)
[tg] Update to Unicode 10.0.0
[tg, selk] Make readonly idempotent
[tg, multiplexd] When truncating the persistent history, do not change the underlying file, do all operations on the locked one; do not stop using the history at all if it has been truncated
[tg, Jörg] Turn off UTF-8 mode upon turning on POSIX mode
[Martijn Dekker, Geoff Clare, many on the Austin list, tg] In POSIX mode, make the exec builtin force a $PATH search plus execve
[tg] Fix GCC 7, Coverity Scan warnings
[tg, Michal Hlavinka] Track background process PIDs even interactive
[tg] Always expose mksh’s hexdump shell function; speed it up by working on the input in chunks; use character classes to make it EBCDIC safe
[tg] Revamp dot.mkshrc default editor selection mechanism

Bug: N/A
Test: builds and boots
Change-Id: I35d624c4352c1b7c1ee499f9680712a30c64323b