commit b90863c0b7b860b006ac49c9396711ff351f777f
Author: Howard Chu <hyc@highlandsun.com>
Date:   Tue Mar 31 13:15:54 2009 +1100

    Add tdb_transaction_prepare_commit()
    
    Using tdb_transaction_prepare_commit() gives us 2-phase commits. This
    allows us to safely commit across multiple tdb databases at once, with
    reasonable transaction semantics
    
    Signed-off-by: tridge@samba.org

Also, actually test locking, rather than just lock count (bit me in samba fix)

struct op: serial -> seqnum (and drop use of term "serial" everywhere).
struct op: op -> type
struct op_desc: general replacement for file/op_num pair.
Change add_dependency to take two const op_desc *: means reshuffle since we can't adjust the args any more.

Add handling of reduced test cases (traverse lines trimmed), and add all the test cases I've been using.

This has proven to be intractible: various attempts to eliminate have failed, so detect at runtime and cease the traversal (and do the remaining ops outside a traverse).

Note: we can still deadlock on traversal vs transaction corner cases.
We handle transactions as single operation, which it logically is.

If we do the trace inside the lock, we show the actual sequence number when the transaction started.

Also changes first member of transaction to have valid start_group field,
and fix outdated comment.

(Invasive: means passing full op array all the way through).