Move mksh to a separate project.

Move mksh to a separate project.

This was originally in system/core/mksh

commit ba2627c6cdb3aaa40aebd362170c382b55b7b511
Author: Thorsten Glaser <tg@mirbsd.org>
Date:   Tue Aug 24 18:21:37 2010 +0200

    Add mksh from CVS 2010/08/24 as system/core/mksh module

    Both shells (ash from system/core/sh, and mksh) are built by
    default but only the one where $(TARGET_SHELL) is set to is
    actually installed (the shell and the mkshrc configuration
    file are tagged shell_mksh for this to work).

commit f41986bbc79055a4feed7266cac5c1b540296daf
Author: Jeff Hamilton <jham@android.com>
Date:   Fri Sep 10 10:46:06 2010 -0500

    Don't alias 'stop' to 'kill -STOP'

    Android has already has a stop command used
    to stop the main runtime and the alias
    interferes with testing tools that expect
    stop to kill the runtime.

Change-Id: I5ddf28dbd0221148d3b8f55eaf4f1e7d046c9288