* all future upgrades will follow this path
* don't check on any trackers when an upgrade is in progress (everything may be locked)
* run the upgrade function from tracker_run()
Merge masters latest changes into the twitterfields branch.
* mysql collation utf8mb4
* new tweet fields (no extra tables, no upgrade table structure yet)
* add five new Twitter fields, set standard database encoding to utf8mb4
* streamline insert functions using Tweet class
* merge with master
* add withheld_in_countries for users and tweets
* fix improper storing of hashtags
* minor changes
* make import-gnip use the new TweetQueue class
* make the search script use the new TweetQueue class
* make lookup.php use TweetQueue class
* empty parms
* small fixes and error reporting for cli tools
* user search; adding a Tweet::isInBin()? function
* import-jsondump.php using TweetQueue
* import-timeline.php using TweetQueue
* we don't have a success indicator for TweetQueue->push()
* these scripts now check explicitely whether a tweet (id) is already in the bin before inserting
* streaming import now adds (multiple) media urls to url table (@todo: gnip import)