This combines two enhancements to the ledger_data RPC
command and related commands.
The ledger_data RPC command will now return the ledger header
in the first query (the one with no marker specified).
Also, ledger_data and related commands will now provide the
ledger header in binary if binary output is specified.
Modified existing ledgerdata unit test to cover new functionality.
When started with "--start", put all known, non-vetoed
amendments in the genesis ledger. This avoids the need
to wait 256 ledgers before amendments are enabled when
testing with a fresh ledger.
This will allow code that looks at the ledger header to know what version the
SHAMap uses. This is helpful for code that rebuilds ledger binary structures
from the leaves.
