improve usability of global ovrlays for write operations; may need to anticipate SLAPI accordingly.  More work needed for add (overlays need to understand they're global and call slap_mods2entry() explicitly)

intercept. Now a single syncprov works over the entire glued context.

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

result to client.

instead of getting a timestamp at the end. This makes it possible for
slurpd to sort the log later.

(slapi_x_XXX is still reserved for exported functions that are not part
of the SLAPI specification)

1) simultaneous operation of multiple active sync replication threads
2) cookie management for individual sync replication thread
   (include rid=%3d to the slapd cookie command line option (-c))