Added a stopwatch class to the Compatibility namespace along with unit tests. On systems that support the System.Diagnostics.Stopwatch, it chains to that class. On systems that do not support Stopwatch, it is implemented with DateTime Ticks.
Add ability to stop test run: update interfaces, implement cooperative stop, still needs work on forced stop
Fix errors from rebase by eliminating forced stop code for now.
Changed the usage of System.Diagnostics.Stopwatch and DateTime in DelayedConstraint to use the NUnit version of Stopwatch.
Visual Studio 2013 insists on adding these changes to the project files to identify them as NUnit test projects. Microsoft does this for performance reasons, see https://connect.microsoft.com/VisualStudio/feedback/details/800245/vs2013rc-adds-to-vs2012-c-project-section-itemgroup.

I am sick of ignoring them, so want to get them locally into the repository.
Add code for cancelling a test; finalize API
Increase wait time for cancellation test so it passes - temp fix till we correct problem with completion event
Add slow-tests to NAnt build
Increased the sleep in the stopwatch tests to a value that is hopefully above the resolution of the Thread.Sleep call.
Cut 20 seconds off the overall test run (on my machine) by reducing the sleeps and delays in DelayedConstraintTests.
Switch other usages of stopwatch over to the NUnit version.
Remove WaitForCompletion from public API. Test events provide the same information.
Advance version to 2.9.7
Update msbuild script to include slow-tests
Fix compiler warnings
Fixes based on review of the pull request
Merge pull request #173 from nunit/feature-stop-run

Feature stop run
Merge pull request #172 from nunit/issue-155

Ongoing changes for Issue 155