Added ability to add sprintf variables to JText string

[writing it up now...]
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Added ability to use custom non-language string as first part (can be used for concatenating other strings)
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
[#30652] Commit for issue 29916 broke Smart Search indexing. Thanks Don
Gilbert.
[#30639] Hathor Tags issues Tag edit view. Thanks Elin Waring.
[#30640] Hathor - Not tag field shown in core content. Thanks Roberto
Sequra.
[#30653] Use of undefined DEBUG constant. Thanks Elin Waring.
[#30603] Tags: Similar Tags Module Shows the same article multiple time.
Thanks Thomas Hunziker.
[#30642] Creating a new Tag based on existing one, using "Save as Copy"
appends a number even the new Title of the copy is different from the
original. Thanks Ashan Fernando.
Prepare for 3.1.0 release
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Prepare for 3.1.1 development
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Fix webdriver tests for change in module edit form (using textarea for
class suffix)
[#30702] Only titles display in featured/blogged views when hide intro
text is selected.
[#30681] Error in Database tab in Extension Manager.
[#30697] Invalid tab end in article edit page. Thanks Dennis Hermatski.