Uses the "Last-Modified" header for "If-Modified-Since"

Uses the "Last-Modified" header for "If-Modified-Since"
see http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.3.4

Change-Id: I0f5e9b45f4f79d7c1b286e465f9750dcd71b6bfd
Signed-off-by: Ralph Bergmann <ralph@the4thfloor.eu>
Merge branch 'temp'