Log Message:
Update shells/mksh to version 30.  Changes from version 29.6 include:

* If the basename of argv[0] starts with "sh", activate FPOSIX early,
  preventing some typical ksh aliases from being defined.

* If FPOSIX, don't pre-define aliases (except integer and local) to
  benefit operating environments that never heard of the great Korn Shell.

* Support x=(a b c) bash-like array initialisation
* Support ${foo:2:3} bash-like substring expansion

* Don't try to execute ELF, a.out, COFF, gzip or MZ binaries, e.g.
  mksh /bin/sh.

* Prefer well-known signal names to alphabetically earlier ones

* Fix a bug delivering ERR and EXIT pseudo-signals to traps combined
  with "set -e".

Update from mirabilos#pkgsrc with small fixups by me.