Add snapshot for DragonFly BSD

[mneumann]

@alexcrichton: The snapshot file is here: http://www.ntecs.de/downloads/rust/rust-stage0-2015-08-11-1af31d4-dragonfly-x86_64-08e7dd9d77434b377c0905cc5f8c705b2daf3a0e.tar.bz2.

This is the first part in getting Continuous builds for DragonFly (#16298).

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+ ebf311c

Thanks! When you get a chance, could you also send me your PGP key on IRC?

[bors]

⌛️ Testing commit ebf311c with merge a53d31a...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[dhuseby]

@mneumann this is really cool. I just set up a dragonfly build bot and was about to do this exact thing when I noticed that there was a snapshot already in the snapshots.txt file. I already run the Bitrig and FreeBSD buildbots. I'm all ready to get DragonflyBSD going. I just need @brson to set up the account and crypto keys.