Add 6.e array multislice fast-path tests
Add 6.e array multislice fast-path tests

All of the tests so far had an explicit (but potentially false)
adverb, which caused always the slow paths to be taken.  Which
obscured a blatant bug yesterday.  This adds tests for the fast
code paths of array multislicing.

dogbert17/roast,perl6/roast,dogbert17/roast