openjdk-7-jre-headless does not satisfy JRE requirement in Debian package

Likewise for openjdk-6-jre-headless and default-jre-headless.

The regular JRE packages pull in Gnome.  On a server it would be much nicer to be able to use the headless versions.

I can work around this issue by installing pusher with:

```
dpkg --force-depends -i buddycloud-pusher_$LATEST_all.deb
```

But when I do that apt-get complains every time I try to install more packages.
