Testing to catch exception for build: http://builds-artifacts.piwik.org/ui-tests.master/2606.1/screenshot-diffs/diffviewer.html

Maybe this fixes the Installation screenshot tests? http://builds-artifacts.piwik.org/ui-tests.master/2600.1/screenshot-diffs/diffviewer.html

Removed installation step 'databaseCheck'
Factored out the System check in its own class
(The 3 strings keys were removed from otrance)

Fixes #5005 Reset the PluginsInstalled array from the config file, so the status is set correctly when re-installing Piwik and creating new tables

refs #1915 reset viewDataTable parameters before each test run to remove previously persisted viewdatatable params from other test runs

Refs #5037 Setting [General] `enabled_periods_UI` can be used to specify which periods are available in the calendar.

`zend_mm_heap corrupted` https://travis-ci.org/piwik/piwik/jobs/24192025
 1) Test_Piwik_ServeStaticFile::test_firstAccessNoCompression https://travis-ci.org/piwik/piwik/jobs/24192027

Error was https://travis-ci.org/piwik/piwik/jobs/24163923

Fixes #2268 Implement a default Referrer spam blacklist to block semalt.com spammer. (can be extended to other spammers on request!)

; All Visits with a Referrer URL host set to one of these will be excluded.
; If you find new spam entries in Referrers>Websites, please report them here: http://dev.piwik.org/trac/ticket/2268
; List of known Referrer Spammers, ie. bot visits that set a fake Referrer field:
referrer_urls_spam = "semalt.com"

This is set to three concurrent processes in core:archive command.
Refs #4903