Fix test 29 for new symtab API
Investigating unfound field "x"

It appears that the copy machinery in copy_extended_tokensym thinks
that it is copying the x token, though it cannot be found during
the struct field lookup.
Found a flaw in anonymous field detection in copy_extended_sym
Found a flow in token value masking in copy_extended_sym
Squashed segfault, back to unknown field