Ports 708_param_shadow_mod, 712_redecl and 961_opaque_guards into
test/tool/rejects_test.ww on testenv, one commit because the three
carriers share the single asymmetric-polarity claim (cstage rejects,
wwstage accepts) that a both-stage //ww:error fixture cannot carry.
The neg_selfimp leg drops: test/wcc/data/r948_selfimport/case.ww owns
the identical both-frontend claim.
Hojun-Cho
16413a4864