The basic idea of the tests are to try to exit the running process by calling
Environment.Exit(int). The entry point, Main, denies UnmanagedCode from being
executed. UnmanagedCode is required to call Environment.Exit(int). Then we try
to call Environment.Exit(int) from other threads which "should" have inherited
the restriction from the "main" (i.e. original) thread.

This security stack "inheritance" is called "stack propagation".


* thread1.cs	Deny unmanaged code before creating the thread object.
* thread2.cs	Deny unmanaged code after creating the thread object but 
		before calling Start.
* thread3.cs	Deny unmanaged code after creating the thread object and 
		calling Start. 

* timer1.cs:	Use System.Threading.Timer (Thread.Start) to test stack 
		propagation.
* timer2.cs:	Use System.Timers.Timer (ThreadPool.QueueUserWorkItem) to test
		stack propagation.