TX script improvements, added features (tx's with both Satoshi and MMGen inputs)
	modified:   mmgen-addrgen
	modified:   mmgen-addrimport
	modified:   mmgen-txcreate
	modified:   mmgen-txsend
	modified:   mmgen-txsign
	modified:   mmgen-walletchk
	modified:   mmgen-walletgen
	modified:   mmgen/addr.py
	modified:   mmgen/config.py
	modified:   mmgen/tx.py
	modified:   mmgen/utils.py