Fix examples/VPC_EC2_Instance_With_Multiple_Dynamic_IPAddresses.py

 - introduces ec2.NetworkInterfaceProperty
 - adds properties to NetworkInterface:
  - SecondaryPrivateIpAddressCount
  - NetworkInterfaceId
  - DeviceIndex
 - makes SubnetId not required
CacheSecurityGroupNames not required if using VpcSecurityGroupIds
Minimal implementation of implicit references
Merge pull request #31 from olark/master

CacheSecurityGroupNames not required if using VpcSecurityGroupIds
Add VPNConnectionRoute object and attribute to VPNConnection
add new CrossZone option to ELB
Add VPC_With_VPN_Connection example
Fixup some of the network related validators and pep8 changes
Add support for Tags and PortRange

This is a bit of a hack but it allowed more direct conversion of
VPC_With_VPN_Connection.template.
Merge pull request #34 from craigbruce/master

add new CrossZone option to ELB
Add more resource name properties per CloudFormation release 2013-12-19
Add Tier Environment property per CloudFormation release 2013-12-19
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
Move resolver.py into __init__.py
Failing test for references in tuples

see https://github.com/cloudtools/troposphere/pull/32#discussion_r8442938
Implement implicit references in tuples

see https://github.com/cloudtools/troposphere/pull/32#discussion_r8442938