Fix unwind passing of functions with 2+ arguments

This is a fixup to 9cb32ac. The original change was only sufficient for
functions taking exactly one argument (such as the `error?` function).

This fixup now correctly handles unwind passing in multi-argument
functions as well (such as `type?` which takes two arguments: one
regular, one refinement):

    >> foo: func [x y] []

    >> foo break 1
    ** Throw error: no loop to break

    >> foo 1 break
    ** Throw error: no loop to break

    >> foo break continue
    ** Throw error: no loop to break

    >> foo continue break
    ** Throw error: no loop to continue

Corresponding tests have been added to the test suite
(rebolsource/rebol-test@87073d4).
Merge pull request rebol/rebol#180 (earl/fix-unwind-passing) into community

* earl/fix-unwind-passing:
  Fix unwind passing of functions with 2+ arguments