Merge pull request #1885 from mthom/setof_bagof_fixes

Fix group_by_variants/4 and keysort in setof/3

diff --cc build/instructions_template.rs
Simple merge

diff --cc src/lib/builtins.pl
Simple merge

diff --cc src/machine/dispatch.rs
Simple merge

diff --cc src/machine/mod.rs
Simple merge

diff --cc src/machine/system_calls.rs
Simple merge