Restore camel-http to be using Http Client 3.1 (was: Move to httpclient 4.1 when it's available)

Currently httpclient 4.0.1 is missing the functionality that allows a user to specify an alternate list of authentication methods, this was re-introduced into httpclient's trunk, however httpclient 4.1 appears to be in alpha currently. When httpclient 4.1 is finally available camel-http should move to that version.