Get rid of EIGEN_TEST_FUNC, unit tests must now be declared with EIGEN_DECLARE_TEST(mytest) { /* code */ }.

This provide several advantages:
- more flexibility in designing unit tests
- unit tests can be glued to speed up compilation
- unit tests are compiled with same predefined macros, which is a requirement for zapcc

test/commainitializer.cpp

@@ -65,7 +65,7 @@ struct test_block_recursion<-1>
   static void run() { }
 };
 
-void test_commainitializer()
+EIGEN_DECLARE_TEST(commainitializer)
 {
   Matrix3d m3;
   Matrix4d m4;