tests: fix %printer.

tests: fix %printer.

Currently, there is no check that %printer ... <foo> (nor
%destructor) is about an existing <foo> type.  This C++ test had
it wrong (<::std::string> vs. <std::string>).

	* tests/c++.at (AT_CHECK_VARIANTS): In list.yy, redefine the
	pretty-printing of lists into something better for parser traces.
	Update the expected output.
	Fix correspondance between %type/%token and %printer.