[PMC] Moved more logic from default PMC's isa_pmc() into Class's isa_pmc(), where we can avoid COW STRINGs in almost every case.  There may be more improvements here, but this change improves Rakudo's "Hello, world!" benchmark by 6.327%.
[PMC] Moved more logic from default PMC's isa_pmc() into Class's isa_pmc(),
where we can avoid COW STRINGs in almost every case.  There may be more
improvements here, but this change improves Rakudo's "Hello, world!" benchmark
by 6.327%.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@41372 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot