Fix for issue #100 - Changes to Tolerance definitions

Created unit tests for Tolerance adding tests for the changes I made plus a few for parts of the class that I felt weren't fully tested.

Renamed Tolerance.Empty to Tolerance.Default and added a Tolerance.Exact which means the default will not be used. I also renamed ToleranceMode.None to Unset to better specify its purpose.

While I was adding the unit tests to the solution, I found that the CollectionsEqualsTests.cs was not included in several of the projects, so I added it.
Merge pull request #104 from nunit/issue-100

Fix for issue #100 - Changes to Tolerance definitions

This looks good to me... Lots of files affected by this small change, so everyone should update.
Merge pull request #101 from nunit/remove-addins

Remove test fixture builders and incorporate into attributes
First changes to build using msbuild
Added msbuild root project
Initial build targets working
Building more target frameworks
shell script for linux
Build using xbuild on Windows for mono
Added Test target
Running tests
Pulled together project names
Running test executables under mono launcher
Fixed compilation error on mono 4.5
MSBuild doesn't support property groups within tasks
Configuration for the managed exe launcher should be after runtime configuration
Some refactorings
Reverted build dir to being named after the framework name for simplicity
Getting new build scripts to feature parity with old ones
Fixed property casing
Added targets for packaging