auto merge of #17753 : aturon/rust/error-interop, r=alexcrichton

This PR:

* Adds the error interoperation traits (`Error` and `FromError`) to a new module, `std::error`, as per [RFC 70](https://github.com/rust-lang/rfcs/blob/master/active/0070-error-chaining.md). Note that this module must live in `std` in order to refer to `String`.

    Note that, until multidispatch lands, the `FromError` trait cannot be
usefully implemented outside of the blanket impl given here.

* Incorporates `std::error::FromError` into the `try!` macro.

* Implements `Error` for most existing error enumerations.

Closes #17747

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 67080f4551f..f10a1d5e5ed 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -218,6 +218,7 @@ pub mod time;
 
 /* Common traits */
 
+pub mod error;
 pub mod from_str;
 pub mod num;
 pub mod to_string;
@@ -257,6 +258,7 @@ mod std {
     pub use hash;
 
     pub use comm; // used for select!()
+    pub use error; // used for try!()
     pub use fmt; // used for any formatting strings
     pub use io; // used for println!()
     pub use local_data; // used for local_data_key!()