More relaxed version number limits

[zouppen]

The library is very picky about its build-dependencies. This makes it hard to use as a part of bigger project. I'd like to see the upper bounds of version requirements to be relaxed or removed completely.

[elliottt]

I'm hesitant to remove all upper bounds completely, and tend to stick to the package versioning policy as a guide for what an acceptable upper bound is. Is there a way that we can stick to the policy, and satisfy your concern about build flexibility?

[zouppen]

This pull request above is the minimal change to avoid rebuilding distribution-provided libraries in Ubuntu Oneiric (and probably in Debian Wheezy). Unfortunately it seems this won't solve the issue with my operating system, which I explained in issue #8.

[elliottt]

Thanks for the pull request, I've merged in your changes.