Network acl support (taking over from #1098)

This adds the unit tests missing from #1098. It includes all their commits, plus a merge with current master, plus my added tests.

It also makes the additions PEP8 compliant, fixes some typos, fixes issues with the egress argument in several functions (making it truly optional and making bool compatible with AWS), and makes the vpc_id argument optional in disassociate_network_acl, forcing another call to AWS if not provided.

Sorry if this isn't the right way to do it; wasn't sure if I should do a direct pull against Boto or against jsmartin's repo.