Rename dec/inc_weak_task_count to inc/dec_live_count and remove register_task/unregister_task. Closes #4768
Add debug info tests
fix typos in sample code, add enum to json encoder, add test case
json bugfixes
tidy
json bugfix
json add enum encoder test case
re-special-case Option in JSON encoding
json tidy
Omit discriminant from nullary univariant enums.

If an enum is isomorphic to unit, there's no need to use any bits to
represent it.  The only obvious reason this wasn't the case was because
the enum could be C-like and have a user-specified discriminant -- but
that value is constant, so it doesn't need to be stored.

This change means that all newtype-like enums have the same size (and
layout) as their underlying type, which might be a useful property to
have, at least in terms of making programs' low-level behavior less
surprising.
core: Remove GenericChan/Port from prelude. Closes #4762
auto merge of #4866 : jld/rust/enum-unitlike, r=graydon

If an enum is isomorphic to unit, there's no need to use any bits to
represent it.  The only obvious reason this wasn't the case was because
the enum could be C-like and have a user-specified discriminant -- but
that value is constant, so it doesn't need to be stored.

This change means that all newtype-like enums have the same size (and
layout) as their underlying type, which might be a useful property to
have, at least in terms of making programs' low-level behavior less
surprising.
rust-mode.el uses the 'cl macros, so it should actually require them

Without this change, rust-mode doesn't work if 'cl hasn't been required
by something else, apparently.  I'm not entirely sure what changed such
that I started seeing this problem instead of not, but maybe the emacs
world has been making progress towards not loading 'cl at runtime if
it's only needed at compile time.
added issue for reference in FIXME
etc: rework of how libuv is integrated into the build

- thanks to work in libuv's upstream, we can call libuv's Makefile directly
with parameters, instead of descending in gyp-uv madness and generating
our own.
rt/std: update of libuv API glue for libuv submodule update
build: tweak rt.mk, as per graydon.. CFLAGS had to stay
build: point libuv at olsonjeffery/libuv, temporarily
build: ifdef for mingw/non-mingw builds
std: strip sillyness from debug comment in iotask teardown