#764 Add a "request" type method to the .Validate class

[Rick McGuire]

Frequently, it is desireable to support arguments where the object is obtained via a request() method call (e.g., request("String") or request("Array")). It would nice if a method was provided on Validate() that does the request and raises an error if the object can't be obtained in the required type.

[Erich]

Code has been committed with [r11908]
Committed additional tests and rexxref documentation with revision [r11944]