Can we reference NUnit in Tool rather than Library folder?

[tillig]

I noticed that in both the core and contrib projects NUnit appears in
two places:
* Resource/Library/NUnit
* Resource/Tool/NUnit

While I see the value in maintaining the set of assemblies referenced
in one place separate from the set of tools used in the build, NUnit
sort of spans that gap. I'm curious if we can switch it to only have
NUnit in the Tool folder and remove the Library folder.

* Keeping them separate introduces the chance that the version you're
building against isn't the version you're executing in the build.
* Keeping them separate means a [slightly] larger working copy
footprint/checkout time.
* Putting them together allows us to add a hook for TestDriven.NET
that will run the actual version in the repository rather than the one
that ships with TestDriven.NET.

Is there any objection to unifying NUnit into one spot (each for core
and contrib)?

[tillig]

Per a note from Nick in issue 241...
http://code.google.com/p/autofac/issues/detail?id=241
...I'll update things to reference the version in the Tool folder (and
make sure everything builds).

-T