Clean up plpgsql identifier handling: process quoted identifiers

Clean up plpgsql identifier handling: process quoted identifiers
correctly, truncate to NAMEDATALEN where needed, allow whitespace
around dots in qualified identifiers.  Get rid of T_RECFIELD and
T_TGARGV token categories, which weren't accomplishing anything
except to create room for sins of omission in the grammar, ie,
places that should have allowed them and didn't.  Fix a few other
bugs en passant.