[perl #116178] [BUG] default-assignment (//-) doesn't mix with implicit-variable method call in Rakudo

[Christian Bartolomaeus via RT]

This works now. I unfudged the existing test and added a second test to 
S03-operators/assign.t
 with commit https://github.com/perl6/roast/commit/fdaa7dc62e

I'm closing this ticket as 'resolved'.