Added the possibility to write graph_format=none, in which case the graphs are...

Added the possibility to write graph_format=none, in which case the graphs are displayed (provided nograph and nodisplay options are not used) but not saved.

DynareBison.yy

@@ -2261,6 +2261,8 @@ allowed_graph_formats : EPS
                         { driver.add_graph_format("fig"); }
                       | PDF
                         { driver.add_graph_format("pdf"); }
+                      | NONE
+                        { driver.add_graph_format("pdf"); }
                       ;
 list_allowed_graph_formats : allowed_graph_formats
                            | list_allowed_graph_formats COMMA allowed_graph_formats
@@ -2705,6 +2707,7 @@ symbol : NAME
        | EPS
        | PDF
        | FIG
+       | NONE
        | DR
        ;
 %%

DynareFlex.ll

@@ -226,6 +226,7 @@ string eofbuff;
 <DYNARE_STATEMENT>eps  {yylval->string_val = new string(yytext); return token::EPS;}
 <DYNARE_STATEMENT>pdf  {yylval->string_val = new string(yytext); return token::PDF;}
 <DYNARE_STATEMENT>fig  {yylval->string_val = new string(yytext); return token::FIG;}
+<DYNARE_STATEMENT>none  {yylval->string_val = new string(yytext); return token::NONE;}
 <DYNARE_STATEMENT>print   		{return token::PRINT;}
 <DYNARE_STATEMENT>noprint   		{return token::NOPRINT;}
 <DYNARE_STATEMENT>conf_sig  		{return token::CONF_SIG;}