It requires the BUSYBOX_SRC environment variable to be set,
and optionally passes arguments to the busybox test runner with
the RUNTEST_ARGS environment variable.
Example:
```
make busytest MULTICALL=1 BUSYBOX_SRC=~/dev/busybox RUNTEST_ARGS=tr
```
Squashed commit of the following:
commit 7b7981d315dd7748287bedc8f6417bbc2f9cb1ee
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Sat May 24 00:33:49 2014 -0400
Last minute touchups
commit dae70f52e2b485695e8c7e2ce8d2997f571afcab
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Fri May 23 23:43:24 2014 -0400
Minor indentation fixes
commit 782a02fe2768cf9e457bb6db9e8a63615c3a4bd1
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Fri May 23 23:40:57 2014 -0400
Fixes for latest rust
commit 51b0e59f75352bf65c89d2ab8cf0948da8404753
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Sun Apr 27 15:15:29 2014 -0400
Fixups
commit 9efd1f4c07f4610e3067a5b2bd047eb117344cdf
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Sun Apr 27 14:20:11 2014 -0400
Basic date and timestamp support
commit a354bc9c07a6ed2cd2748f1734a1ce0f6683e58c
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Sun Apr 27 01:37:37 2014 -0400
Primary functionality in place
commit 8bbaa0caa34fbca129db0c86f32d376d6eafbe18
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Sat Apr 26 22:23:16 2014 -0400
Support creating files
commit 5bf47c3c790b556b596d25a05cd74ca4c06b6d67
Author: Nick Platt <platt.nicholas@gmail.com>
Date: Mon Apr 21 00:24:49 2014 -0400
Add touch with basic usage text
