Support temporary bindings via '?*'

All bindings of pattern variables that start with `?*` should be removed before pattern matching.

That feature eliminates much of the need for various `delete _.bindings["?this"]` statements.

[Plax](https://github.com/Comcast/plax) behaves this way, and it's been helpful in practice.

No file or test is named in the issue. Start by locating the pattern-matching entry point and existing handling for bindings such as `?this`; verify how Plax treats variables beginning with `?*`, then add or update the relevant matching tests so those bindings are absent before matching while other bindings remain available.

Written by the indexing model from the issue text.