The first benchmark shows about twice the throughput of the old system.

Related to issue #2657, but this is not a complete fix.

Incoming

Ports now are represented internally as classes.

Irritatingly, class dtors have a different type from resource
dtors (because class dtors have a self argument), and the monomorphic
case wasn't reflecting that. Fixed.

The fix in 208621 means you now can't shadow a class name with a local,
which is consistent with other behavior. But stackwalk was doing that.
Fixed it.

It wasn't possible to refer to the constructor for a class nested inside
an item from the class's outer scope. Fixed.

The same dtor was getting re-used for different instances, which
didn't always work right. Fixed.

Closes #2642

IMO this is a better workaround than using the old-style
error-pattern: syntax :-)