Ported all the utilities git-annex needs to run on Android: 
git, rsync, gnupg, dropbear (ssh client), busybox. Built a
Makefile that can download, patch, and cross build these from source.

While all the utilities work, dropbear doesn't allow git-annex to use ssh
connection caching, which is rather annoying especially since these systems
tend to be rather slow and take a while to start up ssh connections.
I'd sort of like to try to get openssh's client working on Android instead.
Don't know how realistic that is.

Dealt with several parts of git-annex that assumed `/bin/sh` exists,
so it instead uses `/system/bin/sh` on Android. Also adapted `runshell`
for Android.

Now I have a 8 mb compressed tarball for Android.
Uncompressed it's 25 mb. This includes a lot of git and busybox
commands that won't be used, so it could be trimmed down further.
16 mb of it is git-annex itself.

[[Instructions for using the Android tarball|install/Android]]  
This is for users who are rather brave, not afraid of command line and
keyboard usage. Good first step.
