This replaces the old implementation of asyncrpcoperation_sendmany
with one where all transaction construction is delegated to the
transaction builder. The capabilities of z_sendmany are somewhat
modified in the process:
* z_sendmany now permits sending funds from a Sprout address to
both transparent and Sapling addresses. PRIVACY NOTE: When
user sends a Sprout->Sapling transaction, the amount of the
transaction is publicly revealed.
* z_sendmany no longer supports transactions sending funds into
the Sprout pool, with the exception of change amounts when
sending from a Sprout address.
* When sending transparent coinbase funds to a set of shielded
addresses, the amount sent to recipients must fully consume
the input value and no change is permitted. This is a slightly
weaker constraint than was previously implemented; in the past,
only a single shielded recipient was allowed.
Kris Nuttycombe
Dimitris Apostolou
mdr0id
Marshall Gaucher
Alfredo Garcia
Jack Grigg