Spawn new tasks onto the primary scheduler by default. #3760
Add at_exit function #4450
core: Add private global data interface. #3915
Add `finally` method for deferred execution
core: Add new weak task API
core: Convert getenv/setenv to use a mutex

This much simpler implementation uses a global mutex
and eliminates the kernel environment channel.
std: Convert uv_global_loop to use pipes
core: Remove private::chan_from_global_ptr. #3915
Remove old comm-based weak task interface
core: Stop using oldcomm
replace ConstVector trait with the Container trait
implement Mutable trait for vec
remove remaining is_not_empty functions/methods
Stop using oldcomm in uv_global_loop tests
use mutable function argument syntax in treemap
use mut function argument syntax in priority_queue
Merge pull request #4633 from thestinger/treemap

use mutable function argument syntax in treemap/priority_queue
Merge pull request #4625 from thestinger/container

more little container improvements
doc typo
Revert "Merge pull request #4633 from thestinger/treemap"

I was too hasty in merging -- this needs a snapshot.

This reverts commit 4a7e1ab3745f519536ef6e0377427fc41e47f7c6, reversing
changes made to e447521c1ca2dbead5b485ddc43060b282840817.