This works:
# apt-get install ifenslave
In /etc/modules I put "bonding miimon=250".
In /etc/network/interfaces I put this:
auto bond0
iface bond0 inet static
address 1.2.3.4
netmask 1.2.3.4
gateway 1.2.3.4
up ifenslave bond0 eth0
up ifenslave bond0 eth1
post-down ifconfig eth1 down
post-down ifconfig eth0 down