Add MD5 validation for Amazon SQS.

When available, validates SQS operations against MD5 checksums,
raising errors when there are mismatches.
Configuration toggle for SQS MD5 check.

Adds :sqs_verify_checksums to the AWS config. True by default,
setting this value to false will skip the validation of MD5
checksums for SQS operations.
Remove SQS checksum verification from global config.

Accidentally left the old location of :sqs_validate_checksums
out of the pull request. Removing the old version, tests still
pass.
Merge pull request #332 from aws/sqs-checksum

MD5 Checksum Validation for Amazon SQS
Updated a spec to work with a newer version of rspec.
Loosened the rspec version dependency.
Fixed an issue around configuring endpoints by service region.
Resolved an issue where config might get stuck in a recursive loop.

When building a service endpoint, the region is used to construct the
default endpoint.  When attempting to determine the region, the endpoint
is is parsed (recursive loop).

The recent patch to make endpoint use the svc region instead of the global
region uncovered this bug.  This patch stops the loops by changing the logic
in #svc_endpoint to used only the explicitly configured regions, and never
a region guessed from the endpoint.
Replaced #stub! calls with #stub to silence rspec deprecation warnings.
Add AWS::S3::Client Bucket Logging Methods

Adds the following methods and associated tests:
AWS::S3::Client#get_bucket_logging
AWS::S3::Client#put_bucket_logging

Also adds a method to the Nokogiri Sax Handler to handle comments
in XML by ignoring them.
Add high level methods to AWS::DynamoDB::Table

Adds item_count and size_bytes to the Amazon DynamoDB high level
abstraction layer. Relevant Cucumber and RSpec tests included to
make the process of adding these for later releases a little easier.
Make AWS::DynamoDB::Table tests support 1.8.7

Ruby 1.8.7 doesn't support Time.new with parameters. Using Time.now
instead since that is sufficient for the cases covered.
Deprecated AWS::S3::ObjectMetadata#[]=

Marked AWS::S3::ObjectMetadata#[]= as deprecated and updated documentation
to include a warning note on unexpected changes to metadata and values it
does not set. Updated AWS::S3::S3Object#copy_from documentation to explain
risks of setting metadata hash without copying previous values.

Resolves Issue #325
Make AWS::DynamoDB use legacy client.

The higher level abstractions provided for DynamoDB only work fully with
the legacy version of the low-level client. This change forces the higher
level abstractions to fall back to the legacy client API, but allows use of
the new client-level API directly.
Merge pull request #337 from aws/s3-logging

Add AWS::S3::Client Bucket Logging Methods
Merge pull request #341 from aws/dynamodb-describe

Add high level methods to AWS::DynamoDB::Table
Test failure fixes for DynamoDB.

The way we dealt with the configuration in the previous change on
DynamoDB clients had knock on effects to clients of, for example,
Simple Email Service. Fixed those, and updated tests for DynamoDB
to handle the different way we instantiate its client.
Merge pull request #343 from aws/dynamodb-hl-versioning

Make AWS::DynamoDB use legacy client.
API Update for Amazon EC2

Updates AWS::EC2::Client to support public IPs in VPC, and an optional
dry run flag.
Upgrade AWS::SimpleWorkflow to SigV4