Remove BOOST_PP_IS_EMPTY in favor of BOOST_MPL_PP_TOKEN_EQUAL and added auto as synonym for BOOST_FUSION_ADAPT_AUTO.

Fix ticket https://svn.boost.org/trac/boost/ticket/11157
BOOST_MPL_PP_TOKEN_EQUAL is now used to check if auto/BOOST_FUSION_ADAPT_AUTO
was provided as type, telling to deduce members types.

test/sequence/adapt_assoc_struct.cpp

@@ -57,15 +57,15 @@ namespace ns
   BOOST_FUSION_ADAPT_ASSOC_STRUCT(
       ns::point,
       (x, ns::x_member)
-      (y, ns::y_member)
+      (auto, y, ns::y_member)
       (int, z, ns::z_member)
   )
 
 #else // BOOST_PP_VARIADICS
   BOOST_FUSION_ADAPT_ASSOC_STRUCT(
       ns::point,
-      (BOOST_FUSION_ADAPT_AUTO, x, ns::x_member)
-      (BOOST_FUSION_ADAPT_AUTO, y, ns::y_member)
+      (auto, x, ns::x_member)
+      (auto, y, ns::y_member)
       (int, z, ns::z_member)
   )