Make sigspace after $<var> = binding significant

Doing this required complexifying the grammar some, but in the process I
was at least able to simplify the $<quantified_atom> action
Get tests up to spec
Update bootstrap files with STD-compliant sigspace

Only Parrot and JVM. I cannot currently build NQP on MoarVM, but should
anyone else be willing generate the bootstrap files for it (and please
do), the basic process is:

    git checkout 3b73abb0c src/NQP/Grammar.nqp
    make bootstrap-files
    git checkout -- .

Otherwise, solves GH #140