Define a OUTPUT_BUFFER_SIZE constant in AbstractHttpEntity, which is reused in subclasses.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1463810 13f79535-47bb-0310-9956-ffa450edef68
Add @since tag missing in previous commit for 'Define a OUTPUT_BUFFER_SIZE constant in AbstractHttpEntity, which is reused in subclasses.'

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1463811 13f79535-47bb-0310-9956-ffa450edef68