Merge r1488158, r1488164 from trunk:

mod_session_dbd: Make sure that dirty flag is respected when saving 
sessions, and ensure the session ID is changed each time the session 
changes.


mod_session_dbd: Update the sql query for sessions updates.

Submitted by: minfrin
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1500428 13f79535-47bb-0310-9956-ffa450edef68