Add GCS versioning support.
Merge pull request #1135 from yovadia12/versions

Add GCS versioning support.
Mods to support GCS storage classes
Add update capabilities to DBSnapshot

Conflicts:
	boto/rds/dbsnapshot.py
Support DBSubnetGroupName in RestoreDBInstanceFromDBSnapshot

Conflicts:
	boto/rds/__init__.py
Support None for cookie_expiration_period
Add a convenience create_image method on EC2 Instance objects
1) Changed the Common Request Parameter used to specify the requested operation from
'Action' to 'Operation' to conform to the spec.
2) Modified build_list_params to support both an array of parameter names, or
a string containing a set of whitespace- or comma-delimited parameter names.
Formerly, only a single parameter name could be accepted as a string.
Added support for a number of MTurk features:
1) Added support for SendTestEventNotification operation as send_test_event_notification().
2) Modified create_hit() to support layouts.
3) Added support for GetAssignment operation as get_assignment().
4) Implemented the QualificationRequest class.
5) Now printing out body of response object when debug level is set to 2 in the connection.
Added new module to documentation: boto.mturk.layoutparam
Added new parameters (storage_class, all_versions, and src_generation) to mock_storage_service methods (copy_key, create_bucket, and list_bucket). gsutil's test_commands.py and test_wildcard_iterator.py were failing without this.
Merge pull request #1142 from jterrace/mock-versioning-storage-class-fixes

Fixed mock objects to have new method parameters
[MTurk CLI] Use "h", not "hr", for hours.
[MTurk CLI] Use "www.mturk.com" instead of "mturk.com".

The TLS certificate requires this.
Added exists() to StorageUri for use with the gsutil noclobber feature.
Added exists() to StorageUri for use with the gsutil noclobber feature
Merge pull request #1139 from reversefold/lbcookiestickiness_expirationoptional

Support None for cookie_expiration_period
Merge pull request #1138 from reversefold/instance_create_image

Add a convenience create_image method on EC2 Instance objects
Plumbed headers into the exists methods.
Changed headers to _headers_not_used for the FileStorageUri exists method