Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions

Attached is my work in progress to implement the changes to the CAST() function as proposed by Vik Fearing.

CAST(expr AS typename NULL ON ERROR)

    will use error-safe functions to do the cast of expr, and will return NULL if the cast fails.

CAST(expr AS typename DEFAULT expr2 ON ERROR)
    will use error-safe functions to do the cast of expr, and will return expr2 if the cast fails.