parsergen: include virtual symbols in table of non-terminals

Symbol numbers assigned in grammar_analyse are in three groups:
 - predefined (NUMBER, STRING, etc)
 - Terminals
 - everything else: non-terminals and virtual.

When creating the non_term[] list of names, we need to include
virtual symbols in there, otherwise lookup by symbol-number
might find the wrong value - or might reach beyond end of array.

Signed-off-by: NeilBrown <neil@brown.name>