Fix C# CA1063 warning by implementing the recommended Dispose methods.

Previously just the Dispose() method was generated.
Now the Dispose() and Dispose(bool disposing) methods are generated.
Changes are required if custom "csfinalize", "csdestruct" or "csdestruct_derived"
typemaps are being used. Details in #421 on Github. SWIG will error out if one of
the "csfinalize, "csdestruct" or "csdestruct_derived" typemaps are found. Example
error message:

  foo.h:60: Error: A deprecated csfinalize typemap was found for Foo, please remove
  it and replace all csdestruct, csdestruct_derived and csfinalize typemaps by the
  csdispose, csdispose_derived, csdisposing and csdisposing_derived typemaps.

Closes #421

Examples/test-suite/csharp/allprotected_runme.cs

@@ -13,6 +13,20 @@ public class runme
   {
     MyProtectedBase mpb = new MyProtectedBase("MyProtectedBase");
     mpb.accessProtected();
+    try {
+      // C++ destructor is protected
+      mpb.Dispose();
+      throw new Exception("failed to catch MethodAccessException");
+    } catch (MethodAccessException) {
+      // Exception message: C++ destructor does not have public access
+    }
+    ProtectedDerived pd = new ProtectedDerived("ProtectedDerived");
+    // Destroying via the ProtectedDerived's destructor should work
+    pd.Dispose();
+
+    ProtectedBase pb = new ProtectedDerived("ProtectedDerived");
+    // ProtectedDerived's destructor should be called via the Dispose(disposing) virtual call
+    pb.Dispose();
   }
 }