Refs #3330, #766 add integration test for blob limiting behavior present in certain plugins. Also, fix three bugs:

* CustomVariables plugin does not sort by visit before applying truncation to reports.
* ReplaceSummaryLabel should be recursive so subtables w/ limited rows show 'Others' as label.
* Pass user agent & language explicitly when doing bulk tracking in PiwikTracker.


git-svn-id: http://dev.piwik.org/svn/trunk@6966 59fd770c-687e-43c8-a1e3-f5a4ff64c105