%printer: support both yyo and yyoutput.

lalr1.cc used to support yyo, but not yyoutput.  Support both,
but document only yyoutput (at least until there is some consensus
on this).

* data/c.m4 (yy_symbol_value_print): Also support yyo.
* data/glr.cc  (yy_symbol_value_print_): Support both yyo and yyoutput.
* data/lalr1.cc: Also support yyoutput.
* doc/bison.texinfo: Explicitly use yyoutput in the examples.
* examples/mfcalc/mfcalc.test: Test the -p option.

doc/bison.texinfo

@@ -3155,14 +3155,14 @@ type:
 %code requires @{ #include "type1.h" @}
 %union @{ type1 field1; @}
 %destructor @{ type1_free ($$); @} <field1>
-%printer @{ type1_print ($$); @} <field1>
+%printer @{ type1_print (yyoutput, $$); @} <field1>
 @end group
 
 @group
 %code requires @{ #include "type2.h" @}
 %union @{ type2 field2; @}
 %destructor @{ type2_free ($$); @} <field2>
-%printer @{ type2_print ($$); @} <field2>
+%printer @{ type2_print (yyoutput, $$); @} <field2>
 @end group
 @end example
 
@@ -10244,7 +10244,7 @@ regular destructors.  All the values are printed using their
 @c FIXME: Document %printer, and mention that it takes a braced-code operand.
 @comment file: calc++-parser.yy
 @example
-%printer @{ debug_stream () << $$; @} <*>;
+%printer @{ yyoutput << $$; @} <*>;
 @end example
 
 @noindent