apt: Add backports to sources.list
apt: Use pinning instead of Apt::Default-Release

Setting a default release is useful when two archives (e.g. stable and
testing) are configured, but once a third archive (e.g. unstable) is
added, this gets messy. All no-default archives get chunked together
with the same priority, so once you install a version from any
non-default archive, it will happily upgrade to the most recent version
from another archive.

By giving each archive a separate priority, this shouldn't happen. Since
the version numbers in the archives typically increment in the reverse
order of the priorities, this should do the right thing in most
circumstances.
apt: Pin fish with a higher priority from OBS.

Fish builds deb's on OBS but since we pin wheezy to 990 by default we
weren't getting the updates. This fixes that :).
Merge branch 'template' into mail