Back from vacation, with a message backlog of 181. I'm concentrating first on
low-hanging fruit of easily implemented todos, and well reproducible bugs,
to get started again.

Implemented --batch mode for `git annex get` and `git annex drop`, and also
enabled --json for those.

Investigated git-annex startup time; see
<http://git-annex.branchable.com/todo/could_standalone___39__fixed__39___git-annex_binaries_be_prelinked__63__/>.
Turns out that cabal has a bug that causes many thousands of unnecessary
syscalls when linking in the shared libraries. Working around it halved
git-annex's startup time.

Fixed a bug that caused `git annex testremote` to crash when testing a
freshly made external special remote.
