[pmc] Fixup most WBs [2/2]

:no_wb on non-writers, :manual_wb on VTABLE method calls on SELF which to a WB (avoid duplicates).
See new description at https://github.com/parrot/parrot/issues/1069
Some UNUSED missing.

Still the same 2 regressions:
t/op/gc.t                                 (Wstat: 11 Tests: 19 Failed: 0)
  Non-zero wait status: 11
  Parse errors: No plan found in TAP output
t/pmc/namespace-old.t                     (Wstat: 1024 Tests: 38 Failed: 4)
  Failed tests:  27-30
  Non-zero exit status: 4