[project @ 2002-12-13 16:04:56 by simonmar]

When lexing a primitive string, always make a "narrow" FastString.
Otherwise when the string contains zeros we get a Unicode string,
which luckily turns into the right thing when compiled but confuses the
byte-code generator.

So this fixes the symptom (byte-code generator can't load files
generated with happy -ag), but not the real bug (byte-code generator
can't handle unicode strings).