Change in media scanner to set correct date

When the media scanner scanned a single file, the modified
date (DATE_MODIFIED) was not correctly set in the content
provider. It was set as milliseconds but should have been
set as seconds. This caused downloaded media items to display
wrongly in the camera album, since the date was wrong.

Change-Id: I24cd92215c26f579eb33a4a3890f96c6ef9ec8c0