Re: improve pgbench syntax error messages

> Here is a v3, which (1) activates better error messages from bison
> and (2) improves the error reporting from the scanner as well.

v4.

While adding a basic function call syntax to expressions, a noticed that 
it would be useful to access the "detail" field of syntax errors so as to 
report the name of the unknown function. This version just adds the hook 
(expr_yyerror_detailed) that could be called later for this purpose.

-- 
Fabien.