skeletons: add support for %code epilogue

When building the test cases, emitting code in the epilogue is very
constraining.  Let's make it simpler thanks to %code epilogue.

However, I don't want to document this: it is bad style to use it (we
should avoid having too many ways to write the same thing,
TI!MTOWTDI), just put your code in the true epilogue section.

* data/skeletons/glr.c, data/skeletons/lalr1.d, data/skeletons/lalr1.java,
* data/skeletons/yacc.c: Implement support for %code epilogue.
Remove useless comments.
* tests/calc.at, tests/java.at: Simplify.

tests/java.at

@@ -117,13 +117,8 @@ exp:
 | '-' error          { $$ = new Integer (0); return YYERROR;                }
 ;
 
-]AT_LEXPARAM_IF([[
-%code lexer {
-]],
-[[
-%%
-class CalcLexer implements Calc.Lexer {
-]])[
+]AT_LEXPARAM_IF([[%code lexer {]],
+                [[%code epilogue { class CalcLexer implements Calc.Lexer {]])[
   StreamTokenizer st;
 
   public ]AT_LEXPARAM_IF([[YYLexer]], [[CalcLexer]])[ (InputStream is)
@@ -176,10 +171,9 @@ class CalcLexer implements Calc.Lexer {
     else
       return st.ttype;
   }
-]AT_LEXPARAM_IF([[
+]AT_LEXPARAM_IF([], [[}]])[
 };
-%%]], [[
-}]])[
+%%
 ]AT_JAVA_POSITION_DEFINE[
 ]])
 ])# _AT_DATA_JAVA_CALC_Y