406. Briefly: Missing package in debian wheezy -- forgot apt-pinning settings

In the off-chance that someone for some reason has made the same mistake as I have...

Wheezy is now stable and while that's all fine and dandy, when trying to install tor I kept on getting errors along the lines of

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package tor is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

aptitude show tor

gave

No current or candidate version found for tor
Package: tor
State: not installed
Version: 0.2.3.25-1
Priority: optional

and

apt-cache policy tor

tor:
  Installed: (none)
  Candidate: (none)
  Version table:
     0.2.3.25-1 0
        -10 http://ftp.iinet.net.au/debian/debian/ wheezy/main amd64 Packages

I got similar errors for e.g. wine and virtualbox.
The solution is in the output of apt-cache -- I set up apt-pinning a long time ago (for mpich2?) and forgot about it.

cat /etc/apt/preferences

Package: *
Pin: release a=testing
Pin-Priority: 990

Package: *
Pin: release a=unstable
Pin-Priority: -10

Package: *
Pin: release a=stable
Pin-Priority: -10

Well, wheezy is now stable (and I am tracking wheezy only in my sources.list now) so the problem was quickly solved by simply deleting /etc/apt/preferences.