Add support for NUnit versions > 2.5.3

[jpoehls]

My projects are using NUnit 2.5.4 (or newer) and current I am having to recompile Shouldly using the newer version of NUnit for it to work in my project.

I propose using the solution here to load any version of nunit.framework.dll that is present in the AppDomain.Current.BaseDirectory if the referenced version of NUnit is not found.

I'm willing to submit a patch for this if the powers-that-be agree this is a good solution.

[CoderDennis]

It seems like the commiters on this project are pretty open to pull requests and don't really act like "powers-that-be". And since this is github after all, why don't you just fork the project, implement your solution and submit a pull request?

[jpoehls]

Thanks CoderDennis, I've submitted a pull request in issue #15 for this.

[PandaWood]

Thanks. Yes, I was thinking about this and initially waited for some other wise sage to come in and comment. I'll have a look at the request
It is a big issue for this project, to my mind.
... and I noticed xerxes has made some comments in the pull request - https://github.com/shouldly/shouldly/issues#issue/15

[xerxesb]

Sorry this has taken so long. If anyone is still interested, the latest CI build (v1.0.1.56) has removed the NUnit dependency.

Please grab a copy of the build and test it against your systems :)
http://shouldly.github.com/

As NUnit is now an internal dependency only, this issue is obsolete and will be closed.