Error messages --- now that we've got it, do you like it?

First fruits of all that work on error message rejiggering ...

regression=# \set VERBOSE terse

regression=# select 1!! ;
ERROR:  operator does not exist: integer !!

regression=# \set VERBOSE default

regression=# select 1!! ;
ERROR:  operator does not exist: integer !!
HINT:  No operator matches the given name and argument type(s). You may need to add explicit typecasts.

regression=# \set VERBOSE verbose

regression=# select 1!! ;
ERROR:  42883: operator does not exist: integer !!
HINT:  No operator matches the given name and argument type(s). You may need to add explicit typecasts.
LOCATION:  op_error, parse_oper.c:691

regression=# select 'z' && 'q';
ERROR:  42725: operator is not unique: "unknown" && "unknown"
HINT:  Unable to choose a best candidate operator. You may need to add explicit typecasts.
LOCATION:  op_error, parse_oper.c:684

Before we go too much further, does this look sane to people?
Any adjustments you want to make around the edges?

(BTW, if you're wondering where the 42xxx error codes came from,
I borrowed them from DB2.  The SQL99 spec seems happy to lump
all sorts of conditions under 42000 "syntax error or access
violation" ...)
        regards, tom lane