backporting features to D1

[bearophile]

On a Core Duo, 2 GHz, lot of RAM:

Timigs, best of 3:
  n = 10_000_000:
    D1: 0.14 s  (5.9 X)
    D2: 0.83 s  (1.0 X)
  n = 100_000_000:
    D1: 1.18 s  (6.8 X)  (~1.0 MB RAM)
    D2: 8.04 s  (1.0 X)  (~2.0 MB RAM)

Exe sizes:
  D1: 167.964 bytes
  D2: 165.404 bytes

Bye,
bearophile