Make sure that Joomla is defined or define it!
Remove Joomla namespace
Thanks @Fedik
Update tags.php

When using getTagItemsQuery() in JHelperTags you can specify whether or not to include_children. Setting this to 'true' ends up in a call to getTagTreeArray() (line 511), whereby an attempt is made to instantiate an JTable object (line 642). However, as the include path isn't updated to include the necessary tables folder this fails, and calling the isLeaf() method (line 644) on the supposed JTable results in:

Fatal error: Call to a member function isLeaf() on a non-object in /home/account/public_html/libraries/cms/helper/tags.php on line 647

I think the fix is just to update the include path before the instantiation - tried it on my J! 3.3.6 install and the error disappears.
Initial
Forgot to remove mootools call
progress bar on optimize
[imp]  remove index.html from xml for editors-xtd, editors,
extension/joomla, finder plugins ( Fixes #5399 )
[imp] remove index.html from XML for quickicon, search, system plugins
(Fixes #5400 )
 [imp] Add method="upgrade" for plugins (authentication, captcha and
content) (Fixes #5403 )
[imp]  Add method="upgrade" for plugins (twofactorauth and user) (Fixes
#5406 )
some cs
[imp] Add method="upgrade" for plugins (editors-xtd, editors,
extension/joomla) (Fixes #5409 )
[imp]  Add method="upgrade" for plugins (quickicon, search and system)
(Fixes #5410 )
[fix]  Respect the new values in com_menus Module Assignment (Fixes
#5325 )
Add failing test case for PATH filter
Fix PATH filter
Merge pull request #5413 from mbabker/PathFilterFix

JFilterInput PATH filter does not support a leading slash
Smart Search > Search Filters: moved Delete button. Fixes #5075.

Moved Delete button to the right
See http://issues.joomla.org/tracker/joomla-cms/5062
Smart Search > Content Maps: moved Delete button. Fixes #5074.

Moved Delete button to the right
See http://issues.joomla.org/tracker/joomla-cms/5062