This test was causing problems by using dummy pointers to simulate
connections. When calling the cleanup code, these pointers were
thought to be real, and the code attemtped to clean up threads
referenced by those pointers, causing a segfault.
I've reimplemented the test in the ruby acceptance suite.
While the mirror mutex is taken, the mirroring can be abandoned and serve->mirror
set to NULL, so we need to lock around reading information from serve->mirror
This makes it easier for the tests (and supervisor) to guarantee to be
able to connect to the server socket.
Also this patch moves freeing the mirror supervisor into the server
thread.
