Fix issue with keypair operation in Amazon EC2 service
Update Amazon EC2 API to 2013-06-15
Fixed issue with optional Expires param failing validation

I suspect that makeRequest is making a copy of the params object,
and the delete happens too late in the process. Then validation fails
because Expires is not a valid param.
Lowercase x-amz-security-token header

Fixes #136
Merge pull request #137 from gedefran/master

Fixed issue with optional Expires param failing validation
Disable parameter validation properly in tests
Add test for #137
Fix SiteCatalyst link
Update AWS OpsWorks service
Bump version to v1.4.1