[Rework] Lua API: make the 'orig' address flavour return wire addresses

[Rework] Lua API: make the 'orig' address flavour return wire addresses

Previously task:get_from({'mime', 'orig'}) returned both the preserved
original addresses and the rewritten ones appended by task:set_from,
making the flavour unusable for consumers that need the message as it
arrived (a duplicate-From check would misfire on the combined list, and
Lua could not tell the entries apart). Now, when the 'orig' flavour is
requested and originals were preserved by a rewrite, only the original
addresses are returned; without a rewrite the behaviour is unchanged.

Also expose the 'aliased' and 'original' email address flags to Lua and
document the flavour.