Issue 284 - NUnitLite Unification

This is the  final PR for the umbrella issue we have been calling NUnitLite Unification and fixes #284 

These commits clean up a lot of small things...

  * All source files are now added to every framework build, wrapped by conditions as needed
  * There is no longer a distinction between the nunit and nunitlite frameworks. Only nunit.framework remains.
  * NUNITLITE conditional is now only used to indicate the nunitlite.runner build
  * Where necessary platform conditions (NETCF, SILVERLIGHT, PORTABLE) are used to exclude code
  * Some unused code has been removed

A note on the first point... In the past, we have excluded code from certain builds in two different ways. Sometimes we used a condition. Sometimes we just left the file out of the project. ...And sometimes we did both. This makes it hard to find all the conditions. It's easy to search for #if NETCF but harder to locate all the files not included in the CF build. If we control inclusion of code exclusively by conditions, then it's easier to find all the instances where the code differs by platform.

There are probably still some platform differences we could relax. That can come during later alphas or in the beta phase.

It's definitely true that we could reduce the usage of conditions by centralizing things. That will also have to be at a later point in time.
Same issue with fully qualified names here.  System.Threading namespace exists in all builds, I think.