[PATCH] lib/tdb: TDB_ALLOW_NESTING flag (port from ctdb)

[tridge at samba.org]

Hi Rusty,

I think this is a good patch and it should go in.

Volker, are you happy with this approach? For the example of registry
initialisation that you gave previously (an example of a good use of
transaction nesting btw), you could do this:

  tdb_add_flags(tdb, TDB_ALLOW_NESTING);
  do_some_fancy_initialisation();
  tdb_remove_flags(tdb, TDB_ALLOW_NESTING);

That will give you the speed while still allowing us to prevent this
API oddity from people out like it caught Ronnie.

Cheers, Tridge