librustc: Implement `|A| -> B` syntax for closures and make bare `fn`
work
libstd: Remove mocks.
Make managed_boxes feature gate error less opinionated
Implement a concat!() format extension

This extension can be used to concatenate string literals at compile time. C has
this useful ability when placing string literals lexically next to one another,
but this needs to be handled at the syntax extension level to recursively expand
macros.

The major use case for this is something like:

    macro_rules! mylog( ($fmt:expr $($arg:tt)*) => {
        error2!(concat!(file!(), ":", line!(), " - ", $fmt) $($arg)*);
    })

Where the mylog macro will automatically prepend the filename/line number to the
beginning of every log message.
Fix fallback configuration flags
auto merge of #10206 : brson/rust/configure, r=brson
auto merge of #9740 : alexcrichton/rust/concat, r=cmr

This extension can be used to concatenate string literals at compile time. C has
this useful ability when placing string literals lexically next to one another,
but this needs to be handled at the syntax extension level to recursively expand
macros.

The major use case for this is something like:

    macro_rules! mylog( ($fmt:expr $($arg:tt)*) => {
        error2!(concat!(file!(), ":", line!(), " - ", $fmt) $($arg)*);
    })

Where the mylog macro will automatically prepend the filename/line number to the
beginning of every log message.
auto merge of #10181 : brson/rust/managed_boxes, r=thestinger
auto merge of #10187 : pcwalton/rust/remove-mocks, r=pcwalton

r? @alexcrichton
Rearranged the methods in std::Option and std::Result