Adjust handling of data type names to suppress double quotes

Adjust handling of data type names to suppress double quotes
 unless necessary.
Label internal bpchar types as "character" and varchar types as
 "character varying" to be less Postgres-specific. These types map to
 the SQL92 definitions anyway.
Redefine g_force_quotes to be the local variable force_quotes.
Pass this as an argument to fmtId().
These should help with handling the single-byte internal "char" type.