* [Plugin Library/Setup] The 'Download updates' button in the Plugin Library will now automatically download any updates for all installed plugins.  Previously, it just updated the version information but an admin had to update each plugin by clicking a button in the list.  If a '.git' development directory exists in a plugin then it won't be automatically updated (as this would interfere with development).
* [Plugin Library/Upgrade/Platform] When upgrading from the /update page, Cerb will now attempt to download the latest version of all installed plugins from the Plugin Library.  This should spare admins from having to manually update and re-enable all third-party plugins after an upgrade.
* [Installer/Code Cleanup] Fixed a PHP notice about sessions in the guided installer when adding the first admin account.
* [Plugin Library/Setup] Fixed an issue in the Plugin Library where files from a plugin wouldn't be updated to the latest version if the file had been changed on the disk with a newer timestamp.
Merge branch '6.3.3' into 6.4
6.4-dev checkpoint