updating aws-sdk to 1.18.0

Hello @x-ma, 

Please review the following commits I made in branch 'giannic-awssdk-update'.

8b6b803be827e5f17b37c313a0af2e44cbc4e5d5 (2014-02-18 16:21:22 -0800)
updating aws-sdk to 1.18.0

R=@x-ma