std::rt: require known stack bounds for all tasks.

We just approximate with a 1 or 2 MB stack for native::start.
Renamed Option::map_default and mutate_default to map_or and mutate_or_set
Remove unnecessary substitution of type params when generating
vtable methods before translating the ref to the method itself.
libextra: Introduce typed arenas.

A typed arena is a type of arena that can only allocate objects of one
type. It is 3x faster than the existing arena and 13x faster than malloc
on Mac.
librustc: Move block contexts into per-function arenas, and
stack-allocate function contexts.
doc: Syntax highlight the cheatsheet
doc: Fix table format in cheatsheet
doc: Title guides consistently
mk: Start testing the cheatsheet
doc: Highlight the testing guide correctly
mk: Fix the naming of the windows installer harder

CFG_VERSION includes a bunch of VCS info in it that is not a valid
filename. CFG_RELEASE is just the version number.
Fixed Gc::clone, implemented Gc::ptr_eq
doc: Title reference manual consistently
doc: Fix URL of libextra docs
auto merge of #10854 : Kimundi/rust/result_compose_map_mutate_or, r=alexcrichton

This implements parts of the changes to `Option` I proposed and discussed in this thread: https://mail.mozilla.org/pipermail/rust-dev/2013-November/006254.html, and on IRC.

In short, the string "default" should not be used in any context that has nothing to do with the `std::default::Default` trait.

This PR consists of this change:
- Renamed `map_default -> map_or` and `mutate_default -> mutate_or_set`.
Inline reexports in rustdoc

If a reexport comes from a non-public module, then the documentation for the
reexport will be inlined into the module that exports it, but if the reexport is
targeted at a public type (like the prelude), then it is not inlined but rather
hyperlinked.
'borrowed pointer' -> 'reference'
doc: Add libgreen and libnative to the index
doc: Add rustc and syntax to the index
Address some minor points in the pointer guide

cc #11364.