Make a special remote using adb to send file to an android device.

While there is an android port, a special remote will suffice for many use cases, and may work better overall.

It should support exporttree=yes, since most use cases involve exporting a tree of files and consuming them on the android device.

Use adb push, adb pull, and use adb shell for checkpresent and remove.

Ought to implement import tree too, so that changes made to files on the android device can be imported back into the git repository.

And, export preferred content would be a useful feature for excluding some files from a tree exported to android.

Status: Remote implemented, but not yet import tree and export preferred content. --Joey