libsyntax: Remove the use foo = bar syntax from the language in favor

of `use bar as foo`.

Change all uses of `use foo = bar` to `use bar as foo`.

Implements RFC #47.

Closes #16461.

[breaking-change]

src/libsync/comm/shared.rs

@@ -29,7 +29,7 @@ use rustrt::task::{Task, BlockedTask};
 use rustrt::thread::Thread;
 
 use atomic;
-use mpsc = mpsc_queue;
+use mpsc_queue as mpsc;
 
 static DISCONNECTED: int = int::MIN;
 static FUDGE: int = 1024;

src/libsync/comm/stream.rs

@@ -28,7 +28,7 @@ use rustrt::thread::Thread;
 
 use atomic;
 use comm::Receiver;
-use spsc = spsc_queue;
+use spsc_queue as spsc;
 
 static DISCONNECTED: int = int::MIN;
 #[cfg(test)]