server/tests.at: Make the strace options better.

server/tests.at: Make the strace options better.

  * `-ff' to split the traces for different processes out into separate
    files.  This is mostly good because it removes the confusing
    interleaving of blocking system calls issued from concurrently
    running processes.

  * `-tt' to print high-resolution timestamps on each line, for
    correlating the traces now they've been separated.

  * `-v' to print out full dumps of environments and other such things.

  * `-s1024' to print the whole of longish strings.