rift: Don't check handler's name, check it's type
s3: Added authorization and s3_server binary

Common functionality of s3 and rift servers were splitted to
base_server class.
Added support for AWS aka s3 version 2 authorization API.
Added base skeleton for s3 version 4 authorization API.
Added meta_head - API for requesting for bucket's existence.
s3: Implemented Object PUT handler

Added MD5 checksum verification for AWS authorization mechanism