In DuplexStream explanation: change 'There' to 'The'.

I considered changing FromStr to return a Result<E> parameterized
over an error type E, but I decided that was premature abstraction.
If you want the URL parsing error, call url::from_str() directly.

Intrinsics always want to be inlined.

This depends on the previous fix to not assert.

In certain lvalue code paths, the type of the borrowed value was not
being used to generate temporary spills. I'm a bit surprised we didn't
hit this sooner.

Adds a test case. I had to stare at this one for a bit.

More deprecated mode removal (sort.rs, fun_treemap.rs)