messing around with pipes and stages
Don't generate set_buffer
core: Remove transitional code
std: remove transitional code
syntax: remove transitional code
testsuite: Remove call to set_buffer_, use set_buffer
core/syntax: Add transitional code for pipes
syntax: Make the pipe compiler stop generating set_buffer_ calls
std: Stamp out structural records

See #4665
core/syntax: Staging fixes
auto merge of #4796 : catamorphism/rust/derecord_std, r=catamorphism

See #4665
Merge
Merge branch 'incoming' into removing
Register snapshots
Merge branch 'incoming' into made-snap
Merge branch 'incoming' into removing
Revert "oldmap: use &K instead of K in find and get"

This reverts commit 8e643525d4e5bca993dada43615916c382a0645b.
oldmap: use &K instead of K in find and get

This reverts commit a4250a96fdf61142a9c8dbb6d37ae8435c99e396.

This is not the cause of the nonexhaustive-match failure.