convert ".rktl" test entry points to ".rkt"
fix race in place termination

A place claimed to be done according to `place-wait` before its
clean-up actions ran, including flushing output ports. Fix the
order.
fix `sync` on place with no writers

A `sync` on a place whose initial channel is known to have no writers
could trigger a place result instead of blocking on the place.
raco test: add DrDr-like modes

Run tests in separate processes, support tests in
parallel, flag tests with non-zero exit codes or
stderr output as failing, add timeout support, etc.

Use the `--drdr` flag as a shorthand for DrDr-like flags.
The `--drdr` flag causes `raco test` to check for a `drdr`
submodule, then a `test` submodule, then run the module
directly. (The idea is that DrDr will eventualy try the
same sequence.) A test can declare an alternate timeout
through a `config` sub-submodule (and the idea is that
"props" will go away).
fix some tests