This allows the user to turn it off easily, or only start the assistant and
not the webapp.
I was not able to determine why having runshell run the webapp segfaulted.
Strace was not helpful. Oh well, this is better anyway.
This should avoid relying on features of the Android builtin shell,
and so hopefully avoid failures like this one
http://git-annex.branchable.com/design/assistant/blog/day_197__template_haskell/#comment-07f90830f78f6495dcbdf90eb8636129
The C shim sets up busybox, and uses its builtin shell to run runshell.
It's important that busybox be configured with
CONFIG_FEATURE_SH_STANDALONE, so that while runshell is running, it
does not rely on either system utilities, or busybox being already
installed.
