Misc cleanup

sufficiently configured. Update slapd/slurpd to act appropriately.

  "ABANDON", "STARTTLS", "CANCEL", "WHOAMI", "PASSMOD", "EXT", "INTERM",
  "TLS established", SASL and Extended Response "RESULT".
In Statslog output "conn=xx fd=yy closed", append the reason in
  "()" unless client or server closed the connection after Unbind.
Still missing Statslog output from a number of failed requests.

whoami was crashing for anonymous clients

add exop_is_write() macro for detecting exops that modify a target entry

Misc Clean.

frontend stuff moved into a database structure, essentially to allow overlays to be processed before database selection; passes all tests (ITS#3080)

misc other cleanup