In most cases this involved removing a ~str allocations or clones
(yay), or coercing a ~str to a slice. In a few places, I had to bind
an intermediate Path (e.g. path.pop() return values), so that it would
live long enough to support the borrowed &str.
And in a few places, where the code was actively using the property
that the old API returned ~str's, I had to put in to_owned() or
clone(); but in those cases, we're trading an allocation within the
path.rs code for one in the client code, so they neutralize each
other.
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