long line police
std: various hacking on workcache.
migrate gc.rs to LinearSet
migrate task/spawn.rs to LinearSet
std: Ignore time::tests::test_strptime, it's failing for some reason

I'll file an issue.
migrate coherence.rs to LinearSet
migrate gather_loans.rs to LinearSet
drop is_not_empty from TreeSet/TreeMap
Merge pull request #4585 from thestinger/map

migrate LinearMap<T, ()> to LinearSet<T>
std: un-ignore strptime test; fix bug introduced by 1a226f instead.
Handle divide by zero in constant evaluator
Merge pull request #4586 from thestinger/treemap

drop is_not_empty from TreeSet/TreeMap
Add is_mutbl field to arg
Parse `mut` in arguments
Add is_mutbl field to def_arg
Implement `mut` in arguments
syntax: Allow closure args to be mutable
syntax: Pretty-print `mut` qualifiers on args
testsuite: Add tests for mutable function arguments
doc: Document mutable function arguments