Ported check_const from oldvisit to <V:Visitor> trait API.
Ported check_loop from oldvisit to <V:Visit> trait API.
Port check_match from oldvisit to <V:Visitor> trait API.
Port const_eval from oldvisit to <V:Visitor> trait API.
Ported effect checker from oldvisit to <V:Visitor> trait API.
Port privacy.rs from oldvisit to <V:Visitor> trait.
port reachable.rs from oldvisit to <V:Visitor> trait.
port region.rs from oldvisit to <V:Visitor> trait API.
auto merge of #8539 : pnkfelix/rust/fsk-visitor-vpar-defaults-step2, r=graydon,nikomatsakis

r? @nikomatsakis

Follow up to #8527 (which was step 1 of 5).  See that for overall description 

Part of #7081