Make Pair.new 10% faster for Cool:D => Mu
Make Pair.new 10% faster for Cool:D => Mu

By adding a candidate for Cool:D => Mu.  This candidate *does*
get JITted, whereas the the Mu => Mu candidate isn't.  Otherwise
these two candidates are the same.  Felt like a simple change that
has a lot of benefits, since mostly we're putting using Cool things
as a key in Pairs anyway.

tony-o/rakudo,salortiz/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,labster/rakudo,jonathanstowe/rakudo,labster/rakudo,rakudo/rakudo,nbrown/rakudo,raydiak/rakudo,MasterDuke17/rakudo,awwaiid/rakudo,tbrowder/rakudo,raydiak/rakudo,nbrown/rakudo,samcv/rakudo,lucasbuchala/rakudo,samcv/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,zostay/rakudo,Gnouc/rakudo,softmoth/rakudo,tony-o/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,sjn/rakudo,labster/rakudo,softmoth/rakudo,rakudo/rakudo,softmoth/rakudo,raydiak/rakudo,usev6/rakudo,tony-o/rakudo,nbrown/rakudo,tony-o/rakudo,zostay/rakudo,raydiak/rakudo,tbrowder/rakudo,tbrowder/rakudo,salortiz/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,labster/rakudo,nbrown/rakudo,MasterDuke17/rakudo,softmoth/rakudo,sjn/rakudo,rakudo/rakudo,nbrown/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,softmoth/rakudo,sjn/rakudo,lucasbuchala/rakudo,salortiz/rakudo,usev6/rakudo,awwaiid/rakudo,sjn/rakudo,usev6/rakudo,tony-o/rakudo,salortiz/rakudo,tony-o/rakudo,awwaiid/rakudo,lucasbuchala/rakudo,zostay/rakudo,Gnouc/rakudo,labster/rakudo,samcv/rakudo,samcv/rakudo,usev6/rakudo,zostay/rakudo,usev6/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,sjn/rakudo,rakudo/rakudo,labster/rakudo,rakudo/rakudo,jonathanstowe/rakudo,salortiz/rakudo,Gnouc/rakudo,nbrown/rakudo,samcv/rakudo,tbrowder/rakudo,awwaiid/rakudo,rakudo/rakudo,salortiz/rakudo,awwaiid/rakudo,tbrowder/rakudo