since commit 1db1643 tried to set the default file storage to local files (backed out in a62f694), set the default file storage to "localfile" again and implement the local file download storage writer subroutine which saves downloads to /data/<downloads_id>.gz by default
Properly check for JDK on both older and newer Ubuntus, print out a more explanatory message when not found

This reverts commit 542ee2698106099687970138fcbcc4d13ff8b035.
merge from master
* use data/content/ for storing individual .gz files
* put individual .gz downloads in subdirectories: "<media_id>/<year>/<month>/<day>/<hour>/<minute>[/<parent download_id>]/<download_id>[.gz]"
* cleaned up Tar reader / writer
Merge branch 'master' into RELEASE_20130723
move dump csv files into separate tables to speed queries to core tables
restore from mucked merge