Updated the conda description to refer to features related to packaging.

As per title.
The new wording for the last sentence might give readers the impression conda builds on top of those tools. It might be better to word the last part as a separate paragraph saying something like 'Together with the binstar.org repository hosting service, conda provides a 'cross-platform platform', where the same dependency management system can be used to manage not only Python packages and extensions within an existing Python installation, but also arbitrary external binary dependencies and the Python runtime itself. This allows it to excel at managing the complex dependencies of the scientific Python stack. However, it does this at the cost of reduced integration with the underlying operating system environment, so it may not be suitable for all use cases.".