Set the LD_LIBRARY_PATH when running tests

This way when you disable rpaths you can still run `make check`
extra::json: remove the use of `unsafe` char transmutes.

Avoid using -1 as a char sentinel, when Option<char> is the perfect
thing.
syntax: convert the lexer to use Option<char> over transmute(-1).

The transmute was unsound.

There are many instances of .unwrap_or('\x00') for "ignoring" EOF which
either do not make the situation worse than it was (well, actually make
it better, since it's easy to grep for places that don't handle EOF) or
can never ever be read.

Fixes #8971.
rustc: put range asserts on `char` loads.

A `char` is a Unicode codepoint, and so ranges from 0--0x10FFFF (with
the surrogate gaps): we may as well inform LLVM of this.
rustc: load bools as unsigned numbers.

Apparently loading them signed will break if/when they become i1.
std::fmt: convert the formatting traits to a proper self.

Poly and String have polymorphic `impl`s and so require different method
names.
syntax: remove some dead code.
syntax: convert deriving to take &mut ExtCtxt.
syntax: split out the parsing and the formatting part of format_args!().
Implement `#[deriving(Show)]`.
Update docs and tests for #[deriving(Show)].
auto merge of #12066 : huonw/rust/show2, r=alexcrichton

- Convert the formatting traits to `&self` rather than `_: &Self`
- Rejig `syntax::ext::{format,deriving}` a little in preparation
- Implement `#[deriving(Show)]`
auto merge of #12099 : alexcrichton/rust/rpath-tests, r=thestinger

This way when you disable rpaths you can still run `make check`
auto merge of #12086 : huonw/rust/safe-json, r=kballard

The lexer and json were using `transmute(-1): char` as a sentinel value for EOF, which is invalid since `char` is strictly a unicode codepoint.

Fixing this allows for range asserts on chars since they always lie between 0 and 0x10FFFF.