_sign_string private_key_file can now be file-like

Distribution._sign_string is now a little bit more flexible, allowing
the private_key_file to be a file-like object (or really anything with a
.read() method).
Added support for block device mappings in autoscaling groups (re #753, #1343)
Add missing function parameter (re: #1357)
cloudformation Stack DisableRollback is always True

Fix problem where DisableRollback is always true, because
bool("False") == True
Added "lookup" and "new_item" to dynamodb2.table, which makes it more
compatible with dynamodb.table
Fixed the ability to specify ``logging`` on ``DistributionConfig``.
Fixed up BotoServerException's use of message
Merge remote-tracking branch 'pasc/bdm_for_autoscaling_groups' into develop
Updated a test to match current autoscale output.
Merge remote-tracking branch 'hardys/stack_rollbackfix' into develop
Updated erroneous test.
don't require the price to be a string, and then report 'must be specified' if I pass a float.
add unit tests for InstanceGroup instantation
Merge remote-tracking branch 'seandst/sign_with_file_like_pk' into develop
Fix for Issue#1417

As per :
http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/USVPC_DetachSubnet.html

The API call should be "DetachLoadBalancerFromSubnets" and not "DettachLoadBalancerFromSubnets"
Adding unit test for detach_internet_gateway
pep8 standards
Changing to unittest2
Changing call  to super for setUp
using from clause to import TestCase
Merge branch 'cloudfront-logging' into develop