[Aboriginal] How about ash instead of hush?

[KARBOWSKI Piotr]

Hi Landley, List,

I am utilizing aboriginal as an sysroot+sdk for building static tools 
for the initramfs purposes. So far I have been using only the 1.2.0 
version, which was still based on uClibc.

Right now I do another try to switch to the one with musl and I hit a 
wall with the /bin/sh.

busybox's hush is used as the /bin/sh. The hush does not support 
`readonly`, `command`, or even `set -e` which I was sure is the POSIX SH 
thingy.

Would it be okey to switch to ash in the new aboriginal? Or ship ash as 
dependency (I can alter the /bin/sh symlink on my side). I would be 
happy to send merge request with the needed changes.

-- Piotr.