Change the way that the pending operations are applied to symbol table

parsers.  Instead of trying to find all of them at the start of the top-level
parse, they are recorded in the context, and then applied at the end of the
top-level parse.  The previous technique did not work, simplt because the
top-level parse cannot see all the parser involded -- some are behind rule
firewalls, by design.

Related to #183.
Fixes #204.

include/boost/parser/concepts.hpp

@@ -58,7 +58,8 @@ namespace boost { namespace parser {
         std::declval<int &>(),
         std::declval<ErrorHandler const &>(),
         std::declval<detail::nope &>(),
-        std::declval<detail::symbol_table_tries_t &>()));
+        std::declval<detail::symbol_table_tries_t &>(),
+        std::declval<detail::pending_symbol_table_operations_t &>()));
 
     template<typename T, typename I, typename S, typename GlobalState>
     concept error_handler =