fix typo
Just correct a small typo in spelling of calendar.
 # [#31455] Regression by [#31278]. Thanks Beat (Fix #1536)
Merge pull request #1543 from Achal-Aggarwal/calendar-typo-error

To correct a small typo in spelling of calendar.
Add system tests for components and content. Thanks Puneet Kala.
 # [#31476] Remove unneeded GROUP BY and fix duplicate article display.
Thanks Thomas Hunziker
(Fix #1542)
 # [#31445] Default value tag menu-items. Thanks Constantin Romankiewicz
(Fix #1527)
Fix problem with failing system tests.
 # [#31525] Files uninstall is failing due to missing variable. Thanks
Michael Babker (Fix #1564)
Merge branch 'master' of https://github.com/joomla-projects/joomla-cms
Merge pull request #1568 from alexukf/master

Fix typos
 # [#31496] DEBUG_BACKTRACE_IGNORE_ARGS not supported in PHP
5.3.1-5.3.5. Thanks Beat
(Fix #1566)
 # [#31533] User Interface allows tags in Banner Categories but it
should not. Thanks Elin waring
(Fix #1571)
 # [#31522] No tag fields in hathor - you can't write Tags in component
items. Thanks Elin Waring
(Fix #1567)
 + [#31349] Display Error Message when Magic Quotes is Enabled. Thanks
Brian Teeman
 #+ [#31488] Add Observer pattern to JTable (and use it for Tags
implementation (which also fixes [#31339] too). Thanks Beat.
(Fix #1561)
[#31401] Fixed issue with  object being overwritten by string. (Fix #1446)
[#31319] registration option disabled by default is safer. Thanks Brian
Teeman.
[#31205] Automatically set $db and $app properties on plugins. Thanks
Don Gilbert.
# [#30677] Need to update the readme files. Thanks David Hurley.