c++: move stack<T> inside yy::parser

We used to define such auxiliary structures outside the class, mainly
as a matter of style to keep the definition of yy::parser short and
simple.  However, now there's a lot more code generated inside the
class definition (e.g., all the token constructors), so the
readability no longer applies.

However, if we move stack (and slice) inside yy::parser, then it
should no longer be needed to change the namespace to have multiple
parsers: changing the class name should suffice.

One common argument against inner classes is that they code bloat.  It
hardly applies here, since typically different parsers will have
different semantic value types, hence different actual stack types.

* data/skeletons/lalr1.cc: Invoke b4_stack_define inside yy::parser.

data/skeletons/lalr1.cc

@@ -172,7 +172,6 @@ m4_define([b4_shared_declarations],
 
 ]b4_namespace_open[
 
-]b4_stack_define[
 ]b4_bison_locations_if([m4_ifndef([b4_location_file],
                                   [b4_location_define])])[
 
@@ -339,6 +338,8 @@ m4_define([b4_shared_declarations],
 #endif
     };
 
+]b4_stack_define[
+
     /// Stack type.
     typedef stack<stack_symbol_type> stack_type;