Unwind functions don't propagate from REDUCE

[rebolbot]

Submitted by: BrianH

The unwind functions: RETURN, EXIT, BREAK, CONTINUE, THROW.

The unwinding process doesn't propagate from unwind expressions within the REDUCE code block. If any of the results of those expressions are unwind values then they should be returned instead of the result block. This will allow them to propagate up the call chain.

As it is, the unwind values are just stored in the result block. This is a security hole, and breaks these functions.

This is related to #771, #1509 and #1519. Strangely enough, COMPOSE works properly.

>> reduce [break]
== [make error! 0]
>> compose [(break)]
** Throw error: no loop to break

^{CC - Data [ Version: alpha 110 Type: Bug Platform: All Category: Error Handling Reproduce: Always Fixed-in:r3 master ]}

[rebolbot]

Submitted by: BrianH

Weird: I was expecting QUIT and HALT to be caught by this as well, but they aren't, and not by #1519 either.

[rebolbot]

Submitted by: abolka

Good catch. QUIT and HALT are not affected because they are throws, not unwinds (per the terminology of http://www.rebol.com/r3/notes/errors.html).

[rebolbot]

Submitted by: Ladislav

In the core-tests suite.