This demonstrates some serious failings, which get cleaned up in
following patches.

Author: Volker Lendecke <vl@samba.org>  2010-01-30 03:51:09

    tdb: fix an early release of the global lock that can cause data corruption
    
    There was a bug in tdb where the
    
                    tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
    
    (ending the transaction-"mutex") was done before the
    
                            /* remove the recovery marker */
    
    This means that when a transaction is committed there is a window where another
    opener of the file sees the transaction marker while the transaction committer
    is still fully functional and working on it. This led to transaction being
    rolled back by that second opener of the file while transaction_commit() gave
    no error to the caller.
    
    This patch moves the F_UNLCK to after the recovery marker was removed, closing
    this window.

Add more logging.

Unlike the upstream, we don't have a stable ABI/API.

   tdb: add TDB_DISALLOW_NESTING and make TDB_ALLOW_NESTING the default behavior
    
    We need to keep TDB_ALLOW_NESTING as default behavior,
    so that existing code continues to work.
    
    However we may change the default together with a major version
    number change in future.
    
    metze
    (cherry picked from samba commit 3b9f19ed919fef2e88b2f92ae541e07bc7379cd1)
Signed-off-by: Stefan Metzmacher <metze@samba.org>

    tdb: always set tdb->tracefd to -1 to be safe on goto fail
    
    metze
    (cherry picked from samba commit 85449b7bcc4bd7948bea38b5514a02357950a002)
Signed-off-by: Stefan Metzmacher <metze@samba.org>

    tdb: reset tdb->fd to -1 in tdb_close()
    
    So that erroneous double tdb_close() calls do not try to close() same
    fd again. This is like SAFE_FREE() but for fd.
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    (cherry picked from samba commit b4424f8234a78a79fb2d71d46ca208b4f12e0f9e)
Signed-off-by: Stefan Metzmacher <metze@samba.org>

    tdb: detect tdb store of identical records and skip
    
    This can help with ldb where we rewrite the index records
    (cherry picked from samba commit d4c0e8fdf063f88032c32de7ece60d502b322089)
Signed-off-by: Stefan Metzmacher <metze@samba.org>

    tdb: rename 'struct list_struct' into 'struct tdb_record'
    
    metze
    (cherry picked from samba commit 3b62e250c066f44d0ab08a7db037b6b4f74a914b)
Signed-off-by: Stefan Metzmacher <metze@samba.org>

(Also, remove bogus test dependency for hdr include check)

Offer to run debugger when test fails, with breakpoint.

Add test for non-mmap tdbs.