Also adds proper checking for cont/break being inside a loop.

Closes #1854
Issue #1619

And remove spurious fails/unreachable() calls.

This mod only had two functions, all of whose users have been changed
to use the uint module.

Closes #1931

Instead, use vec::to_mut/from_mut to transform vectors in place as
needed.

Closes #1849

rename char_len_range -> substr_len_chars

Now that core exports "option" as a synonym for option::t, search-and-
replace option::t with option.

The only place that still refers to option::t are the modules in libcore
that use option, because fixing this requires a new snapshot
(forthcoming).

rename str::loop_chars_sub to str::substr_all, and
propagate this change to std::rope and rustdoc's calls to these

To match the init_fn() and init_fn_mut() changes.

Does what it says on the tin.

The next commit will remove support for this syntax.

This commit allows patterns like:

alt x { some(_) { ... } none { } }

without the '.' after none. The parser suspends judgment about
whether a bare ident is a tag or a new bound variable; instead,
the resolver disambiguates.

This means that any code after resolution that pattern-matches on
patterns needs to call pat_util::normalize_pat, which consults
an environment to do this disambiguation.

In addition, local variables are no longer allowed to shadow
tag names, so this required changing some code (e.g. renaming
variables named "mut", and renaming ast::sub to subtract).

The parser currently accepts patterns with and without the '.'.
Once the compiler and libraries are changed, it will no longer
accept the '.'.

will guarantee they have unit type.

Sorry for the pedantry. I was handling a compilation bug related to this code,
and it just jumped out at me.