A few moves/changes following previous patch review

A few moves/changes following previous patch review

* Makefile: Compile tests with TEST defined (to include System.Web.Util.
MachineKeySectionUtils unit tests)
* System.Web.dll.sources: Move MachineKeySectionUtils.cs from System.
Web.Configuration_2.0 to System.Web.Util
* System.Web_test.dll.sources: Move MachineKeySectionUtilsTest.cs from
System.Web.Configuration_2.0 to System.Web.Util

* System.Web.Configuration_2.0/MachineKeySection.cs: Adjust using
clauses. Uncomment some code. Fix TripleDES versus 3DES for Validation
under NET_4_0. Remove 'private' on fields/methods.
* System.Web.Handlers/AssemblyResourceLoader.cs: Adjust using clauses
* System.Web.Security/MembershipHelper.cs: Adjust using clauses
* System.Web.Security/RolePrincipal.cs: Adjust using clauses
* System.Web.SessionState_2.0/SessionId.cs: Adjust using clauses
* System.Web.UI/LosFormatter.cs: Adjust using clauses.
* System.Web.Util/MachineKeySectionUtils.cs: Moved from System.Web.
Configuration_2.0. Rename namespace and remove 'internal' on type
declaration

* Test/System.Web.Util/MachineKeySectionUtilsTest.cs: Moved from Test/
System.Web.Configuration/MachineKeySectionTest.cs. Add test case for
TripleDES versus 3DES