xdmf

[Nico Schlömer <nico.schloemer@gmail.com>]

I was just going to start tinkering with XDMF [1] when I found that specified Git repo [2] won't check out,

```

warning: remote HEAD refers to nonexistent ref, unable to checkout.

```

Perhaps this can be fixed. (I'd like to add CMake exports from XDMF for the new VTK7 package.)

Cheers,

Nico

[1] https://tracker.debian.org/pkg/xdmf

[2] git://anonscm.debian.org/debian-science/packages/xdmf.git