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/conservative_resize.cpp

@@ -109,7 +109,7 @@ void run_vector_tests()
   }
 }
 
-void test_conservative_resize()
+EIGEN_DECLARE_TEST(conservative_resize)
 {
   for(int i=0; i<g_repeat; ++i)
   {