checking in the test for #2427

Note that this test depends on some things from larkost/1402-make-rql-test-friendly-2 that have not yet made it to next
Proof-of-Concept fix for #2427

This puts the socket for each connection into a thread-local storage, allowing a single connection object to serve multiple threads simultaneously. It is not a complete solution as methods like `close()` have not been handled and the cursor cache might not make sense.