sel/bres.c (zap): Don't scramble the freelist when a query is aborted.
If a query is aborted after it's been committed to a server process,
then we kill the server and return its control block to the freelist.
Unfortunately, the function which does this, `zap', unconditionally
tries to unlink the control block from its current position in the
freelist; but it wasn't actually there before. The result is that
another server control block might be linked back into the freelist.
Attaching a second client to it while it's already in use fails when
`attach' tries to remove the server's idle timer, which isn't active: at
this point, we get a segfault.
~mdw / mLib / commit