Fix examples/VPC_EC2_Instance_With_Multiple_Dynamic_IPAddresses.py

 - introduces ec2.NetworkInterfaceProperty
 - adds properties to NetworkInterface:
  - SecondaryPrivateIpAddressCount
  - NetworkInterfaceId
  - DeviceIndex
 - makes SubnetId not required
Add VPNGatewayRoutePropagation per CloudFormation release 2013-11-22
Add Tags properties  per CloudFormation release 2013-09-24
Remove unneeded imports to pass pyflakes
Merge branch 'fix_VPC_EC2_Instance' of https://github.com/fungusakafungus/troposphere into fungusakafungus-fix_VPC_EC2_Instance
Add network changes from CloudFormation release 2013-09-17

- Add PrivateIpAddressSpecification and NetworkInterfaceProperty
- Split up NetworkInterface and NetworkInterfaceProperty
- Add PrivateIpAddresses and SecondaryPrivateIpAddressCount to
  NetworkInterface