Align scoping on errors for easier comprehension

[mdinger]

Deeply scoped errors are difficult to compare. Align them so they're easier to compare.
This errors:

fn test() -> Option<int> {
    Ok(7) // Should be Some(7)
}
fn main(){ 
    test();
}

The error:

<anon>:2:5: 2:10 error: mismatched types: expected `core::option::Option<int>`, found `core::result::Result<_, _>` (expected enum core::option::Option, found enum core::result::Result)
<anon>:2     Ok(7)
             ^~~~~
error: aborting due to previous error
playpen: application terminated with error code 101

Change the error to this or something similar:

<anon>:2:5: 2:10 error: mismatched types: expected `core::option::Option<int>`,
                                             found `core::result::Result<_, _>`
                                     (expected enum core::option::Option,
                                         found enum core::result::Result)
<anon>:2     Ok(7)
             ^~~~~
error: aborting due to previous error
playpen: application terminated with error code 101

[mdinger]

Also, applying highlighting would probably be helpful:

[reem]

There should also be backticks around either both or neither set of types, not just one.