PNUnit-Changes - NUnit 2.5.6

For NUnit 2.5.6, PNUnit has been re-ported from the latest code published on the
Codice Software site, which uses NUnit 2.2.5. This is a minimal port, so as to 
as close to possible to the Codice public release. 

This file documents changes made in porting the code.

1. The codice license file is located in the PNUnit directory.

2. The four Visual Studio projects have been renamed using a pnunit- prefix.

3. NUnit references have been changed to version 2.5.6

4. Code changes to build and run using NUnit 2.5.6 are made using conditional
compilation (#if NUNIT_2_5) to make it easier to locate and backport the changes 
to the Codice version of the code. Some specific changes are listed here.

  4.1 Ambiguous references (TestInfo) and missing classes (TestCase,
      TestSuiteResult, TestCaseResult) are handled using aliases. 

  4.2 PNUnitTestResult has AllTestsExecuted removed.

  4.3 Agent.Main() now starts the Services required for running tests.

  4.4 PNUnitTestRunner has a number of changes:
      * Inherits directly from MarshalByRefObject and overrides InitializeLifetimeService
      * Creates a TestPackage and uses it to set options for the run
      * Uses a TestFilter to select the individual test to run
      * Uses the updated EventListener interface
