Migrate from pdksh to mksh

See https://bugs.debian.org/792110

mksh (50f-1) unstable; urgency=low

  The pdksh transitional package is gone after two full
  releases – pdksh was last in oldoldoldstable.

  The /bin/mksh binary no longer inspects argv[0] to enable
  POSIX and kludge modes when called as sh; use mksh-static
  (as sh and user shell for initrd) or lksh (as /bin/sh on
  general systems) instead.

 -- Thorsten Glaser <tg@mirbsd.de>  Sun, 19 Apr 2015 23:08:08 +0200

Signed-off-by: Osamu Aoki <osamu@debian.org>

README.md

@@ -62,9 +62,9 @@ Cygwin                              | user      | unknown
 
 * Bourne Shell (__sh__)
 * BASH - GNU Bourne Again SHell (__bash__)
-* DASH (__dash__)
-* Korn Shell (__ksh__)
-* pdksh - Public Domain Korn Shell (__pdksh__)
+* DASH - Debian Almquist Shell (__dash__)
+* Korn Shell - AT&T version of the Korn shell (__ksh__)
+* mksh - MirBSD Korn Shell (__mksh__)
 * zsh - Zsh (__zsh__) (since 2.1.2) _please see the Zsh shell errata for more information_
 
 See the appropriate Release Notes for this release
@@ -479,7 +479,7 @@ Notes:
 
 1. Line numbers are not supported in all shells. If a shell does not support
    them, no errors will be thrown. Supported shells include: __bash__ (>=3.0),
-   __ksh__, __pdksh__, and __zsh__.
+   __ksh__, __mksh__, and __zsh__.
 
 ### <a name="test-skipping"></a> Test Skipping
 

test_runner

@@ -25,7 +25,7 @@
 RUNNER_LOADED=0
 
 RUNNER_ARGV0=`basename "$0"`
-RUNNER_SHELLS='/bin/sh ash /bin/bash /bin/dash /bin/ksh /bin/pdksh /bin/zsh'
+RUNNER_SHELLS='/bin/sh ash /bin/bash /bin/dash /bin/ksh /bin/mksh /bin/zsh'
 RUNNER_TEST_SUFFIX='_test.sh'
 true; RUNNER_TRUE=$?
 false; RUNNER_FALSE=$?