Remove rust_unwind.h

Adds the required definitions in the correct place.
Merge branch 'incoming' of git://github.com/mozilla/rust into unwind-fix
Fix incorrect replacement of `modulo` with `rem`
Move impls of `Num` out of core::num and clean up imports
Use #[cfg(not(stage0))] to exclude items from stage0

As requested on the mailing list: https://mail.mozilla.org/pipermail/rust-dev/2013-April/003713.html
Rename Natural to Integer

'Natural' normally means 'positive integer' in mathematics. It is therefore strange to implement it on signed integer types. 'Integer' is probably a better choice.
Use borrowed pointers for Integer methods

This brings them in line with the quot and rem traits, and is be better for large Integer types like BigInt and BigUint because they don't need to be copied unnecessarily.
Add Fractional, Real and RealExt traits
add a Counter iterator
core: Comments only -- move FIXME to correct location
rustpkg: update README saying which tests pass
rustpkg: Make path searching work as described in the rustpkg doc

rustpkg now searches for package directories in ./src rather than
in . . I also added a rudimentary RUST_PATH that's currently
hard-wired to the current directory. rustpkg now uses src/, lib/,
and build/ directories as described in the manual.

Most of the existing test scenarios build now; the README file
(in a separate commit) explains which ones.
rustpkg: Correct directory structure in test scenarios
rustpkg: Preliminary work on install command

Mostly just tests (that are ignored); install command is still
stubbed out.
auto merge of #6051 : thestinger/rust/iterator, r=catamorphism,pcwalton
Restore Round trait and move appropriate methods out of Real
Update impl of Round for Ratio
Add basic documentation for with_capacity
Move documentation for vec::windowed where it will be generated
Rename vec::mod2 to vec::mod_zip