Remove outdated unreachable check from `call_visit_glue`

`call_visit_glue` is only ever called from trans_intrinsic, and the
block won't be unreachable there. Also, the comment doesn't make sense
anymore. When the code was introduced in 38fee9526a the function was
also responsible for the cleanup glue, which is no longer the case.

While we're at it, also fixed the debug message to output the right
function name.
Correct plural of arguments in format_args!
Special case for 0 arguments given in format!
Remove the unneeded final parameter from call_visit_glue

call_visit_glue() is only ever called with None as its last argument, so
we can remove it as well.
core: Stabliize core::cmp

Mark Eq, PartialEq, Ord, PartialOrd as unstable: they will change
slightly after trait reform. Equiv as experimental: better solutions
are desired. min/max stable.
std: Stabilize default

All stable.
alloc: Stabilize rc module.

Weak pointers experimental. Most everything else stable.
std: Stabilize task module.

Most stable. deschedule/failing experimental because of concerns about
naming and desirability.

Adds task::name() to replace deprecated task::with_name().
Fix typo.
Document some trait methods.
Implement FromBase64 for &[u8].

The algorithm was already based on bytes internally.

Also use byte literals instead of casting u8 to char for matching.
Fixed lifetimes on syntax deriving structs, implemented Clone
Correctly stringify! types and paths inside macros

Closes #8709
auto merge of #15784 : dotdash/rust/unreach, r=luqmana

`call_visit_glue` is only ever called from trans_intrinsic, and the
block won't be unreachable there. Also, the comment doesn't make sense
anymore. When the code was introduced in 38fee9526a the function was
also responsible for the cleanup glue, which is no longer the case.

While we're at it, also fixed the debug message to output the right
function name.
auto merge of #15785 : treeman/rust/fix-15780, r=alexcrichton

Fix for #15780.
Implement new mod import sugar

Implements RFC #168.
small typo
auto merge of #15797 : brson/rust/taskstab, r=alexcrichton

Summary:

* alloc::rc module stable
* Rc type stable
* Functions relating to weak references experimental
* core::cmp module stable
* PartialEq/Eq/PartialOrd/Ord unstable because trait reform will make them change again
* Equiv experimental because there may be better sol'ns
* lexical_ordering deprecated because it can be done trivially with the Ord trait
* min/max stable
* std::task module stable
* TaskBuilder::stdout/stderr experimental because we aren't certain we want to configure the environment this way
* try_future experimental because Future is experimental
* try unstable because the error type might change
* deschedule/failing unstable

The major thing I did differently than previously-discussed is that I made `try` experimental: there's been discussion that the error type `Box<Any + Send>` is not sufficient.


Per https://github.com/rust-lang/meeting-minutes/blob/master/Meeting-API-review-2014-07-16.md.
auto merge of #15803 : omp/rust/master, r=alexcrichton

Fix small typo in guide.
auto merge of #15814 : kvark/rust/ast, r=huonw

Makes working with syntax deriving a bit more pleasuring. For instance, once can use local (non-static) strings anywhere inside `TraitDef` now.