Add MDB_APPEND+putmulti() to dirtybench.py.

ok.  1.7 million entries per second in append putmulti mode.  i think
i can live with that.  even when modifying to a 100 byte "big" record
it's 778,623 records/sec.

l.

permutate 787372 words avglen 13 took 0.86sec
stat: {'branch_pages': 0L, 'leaf_pages': 0L, 'overflow_pages': 0L,
'psize': 4096L, 'depth': 0L, 'entries': 0L}
2.15s (365969/sec)
done all 787372 in 4.01s (196292/sec)

stat: {'branch_pages': 101L, 'leaf_pages': 10554L, 'overflow_pages':
0L, 'psize': 4096L, 'depth': 3L, 'entries': 787372L}

k+v size 21109.29kb avg 27, on-disk size: 42216.00kb avg 54
enum 787372 (key, value) pairs took 0.11 sec
reverse enum 787372 (key, value) pairs took 0.10 sec
rand lookup all keys 0.76 sec (1034219/sec)
per txn rand lookup+hash all keys 1.05 sec (746980/sec)
rand lookup+hash all keys 0.81 sec (970370/sec)
rand lookup all buffers 0.75 sec (1053762/sec)
rand lookup+hash all buffers 0.79 sec (998607/sec)
rand lookup all buffers (cursor) 0.78 sec (1014071/sec)
enum 787372 (key, value) buffers took 0.08 sec
get+put all 787372 in 1.30s (604116/sec)
replace all 787372 in 1.15s (682000/sec)

Signed-off-by: David Wilson <dw@botanicus.net>