Since we are using the Open Build Service, we rely on them adding recent
distributions into their build system. However, Distributions are only added
after they are released (with the exception of openSUSE which is created
there).
If you want to test with an unreleased distribution (in your case Debian 7),
you can always
A) build binaries from the sources on your own or
B) try to build a package using your distribution's mechanisms and the source
packages available e.g. here:
http://download.opensuse.org/repositories/home:/xtreemfs/Debian_6.0/
There you'll find the Debian-typical triplet xtreemfs_1.4.[diff.gz|dsc|
orig.tar.gz] to build a package.
Due to Debian's naming of the boost packages, our .dsc file probably needs to
be adapted though.
Anyway, even without a package you can evaluate xtreemfs on Debian 7 now with
solution A.
Nico