Implement Add on Option types

This will allow you to use the + operator to add together any two
Options, assuming that the contents of each Option likewise implement
+. So Some(4) + Some(1) == Some(5), and adding with None leaves the
other value unchanged.

This might be monoidic? I don't know what that word means!
Fix std::getopts::opts_present() to check value.

Currently the opts_present() function only checks to see if the option is
configured in the match, but doesn't actually check to see if the option
value has been set.  This means that opt_present('h') may return false while
opts_present([~'h']) returns true.

Add a test case to catch this condition and fix opts_present() to check
the value before returning true.

Note, there is another API difference between these two functions that this
does not address.  Currently if you pass a non-configured option to
opt_present() the program will fail!(), but opts_present() simply returns
false.  If it is acceptable to standardize on the fail!() then opts_present()
should probably be implemented in terms of the opt_present() function.
core: Add context switching for ARM and MIPS

ARM definitely compiles
Copy libsyntax from local Rust to stage0.

The local_stage0 script was not updated after commit 7dcbaed renamed
librustsyntax to libsyntax, so builds using local Rust fail due to
missing libsyntax.
auto merge of #5328 : bstrie/rust/optadd, r=graydon

This will allow you to use the `+` operator to add together any two
Options, assuming that the contents of each Option likewise implement
`+`. So Some(4) + Some(1) == Some(5), and adding with None leaves the
other value unchanged.

This might be monoidic? I don't know what that word means!
auto merge of #5333 : brson/rust/context, r=brson

ARM definitely compiles
auto merge of #5335 : larryv/rust/local_stage0-libsyntax, r=luqmana

The `local_stage0.sh` script was not updated after commit 7dcbaed renamed
librustsyntax to libsyntax.

Currently, `./configure --enable-local-rust --local-rust-root=FOO && make` will
fail due to the missing libsyntax; this change corrects this.
auto merge of #5317 : luqmana/rust/inline-asm, r=graydon

```Rust
#[cfg(target_os = "macos")]
fn helloworld() {
    unsafe {
        asm!(".pushsection __RODATA, __rodata
                  msg: .asciz \"Hello World!\"
              .popsection
              movq msg@GOTPCREL(%rip), %rdi
              call _puts");
    }
}

#[cfg(target_os = "linux")]
fn helloworld() {
    unsafe {
        asm!(".pushsection .rodata
                  msg: .asciz \"Hello World!\"
              .popsection
              movq msg@GOTPCREL(%rip), %rdi
              call puts");
    }
}

fn main() {
    helloworld();
}
```

```
% rustc foo.rs
% ./foo
Hello World!
```
auto merge of #5329 : wanderview/rust/std-getopts-opts_present, r=graydon

Currently the opts_present() function only checks to see if the option is
configured in the match, but doesn't actually check to see if the option
value has been set.  This means that opt_present('h') may return false while
opts_present([~'h']) returns true.

Add a test case to catch this condition and fix opts_present() to check
the value before returning true.

Note, there is another API difference between these two functions that this
does not address.  Currently if you pass a non-configured option to
opt_present() the program will fail!(), but opts_present() simply returns
false.  If it is acceptable to standardize on the fail!() then opts_present()
should probably be implemented in terms of the opt_present() function.
syntax: implement #[deriving] meta-attribute
auto merge of #5320 : apasel422/rust/metaderive, r=graydon

This is the first in a series of patches I'm working on to clean up the code related to `deriving`. This patch allows

```
#[deriving_eq]
#[deriving_iter_bytes]
#[deriving_clone]
struct Foo { bar: uint }
```
to be replaced with:
```
#[deriving(Eq, IterBytes, Clone)]
struct Foo { bar: uint }
```
It leaves the old attributes alone for the time being.

Eventually I'd like to incorporate the new closest-match-suggestion infrastructure for mistyped trait names, and also pass the sub-attributes to the deriving code, so that the following will be possible:
```
#[deriving(TotalOrd(qux, bar))]
struct Foo { bar: uint, baz: char, qux: int }
```
This says to derive an `impl` in which the objects' `qux` fields are compared first, followed by `bar`, while `baz` is ignored in the comparison. If no fields are specified explicitly, all fields will be compared in the order they're defined in the `struct`. This might also be useful for `Eq`. Coming soon.
Inline asm exprs should be RvalueStmtExpr.
Actually pass inline asm operands around.
Properly handle input operands for inline asm.
Initial support for output operands in asm.