Various things that don't work on Android are just ifdefed out.
* the webapp (needs template haskell for arm)
* --include and --exclude globbing (needs libpcre, which is not ported;
probably I'll make it use the pure haskell glob library instead)
* annex.diskreserve checking (missing sys/statvfs.h)
* timestamp preservation support (yawn)
* S3
* WebDAV
* XMPP
The resulting 17mb binary has been tested on Android, and it is able to,
at least, print its usage message.
This adds a dep on haskell's async library, but since that's been
added to the recent haskell platform release, it should not be
much hardship to my poor long-suffering library chasing users.
