Bring back the constructor-enabled enable_shared_from_this as enable_shared_from_this2.

[SVN r51912]

test/Jamfile.v2

@@ -56,5 +56,6 @@ import testing ;
           [ run sp_recursive_assign2_test.cpp ]
           [ run sp_recursive_assign_rv_test.cpp ]
           [ run sp_recursive_assign2_rv_test.cpp ]
+          [ run esft_constructor_test.cpp ]
         ;
 }